1 | <p align="center">
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2 | <img src="media/logo.png" width="300">
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3 | <br>
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4 | <br>
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5 | </p>
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6 |
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7 | [![Coverage Status](https://codecov.io/gh/sindresorhus/ow/branch/master/graph/badge.svg)](https://codecov.io/gh/sindresorhus/ow) [![gzip size](https://badgen.net/bundlephobia/minzip/ow)](https://bundlephobia.com/result?p=ow) [![install size](https://packagephobia.now.sh/badge?p=ow)](https://packagephobia.now.sh/result?p=ow)
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8 |
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9 | > Function argument validation for humans
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10 |
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11 | ## Highlights
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12 |
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13 | - Expressive chainable API
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14 | - Lots of built-in validations
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15 | - Supports custom validations
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16 | - Automatic label inference in Node.js
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17 | - Written in TypeScript
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18 |
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19 | ## Install
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20 |
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21 | ```
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22 | $ npm install ow
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23 | ```
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24 |
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25 | ## Usage
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26 |
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27 | *If you use CommonJS, you need to import is as `const {default: ow} = require('ow')`.*
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28 |
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29 | ```ts
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30 | import ow from 'ow';
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31 |
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32 | const unicorn = input => {
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33 | ow(input, ow.string.minLength(5));
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34 |
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35 | // …
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36 | };
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37 |
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38 | unicorn(3);
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39 | //=> ArgumentError: Expected `input` to be of type `string` but received type `number`
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40 |
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41 | unicorn('yo');
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42 | //=> ArgumentError: Expected string `input` to have a minimum length of `5`, got `yo`
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43 | ```
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44 |
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45 | We can also match the shape of an object.
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46 |
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47 | ```ts
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48 | import ow from 'ow';
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49 |
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50 | const unicorn = {
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51 | rainbow: '🌈',
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52 | stars: {
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53 | value: '🌟'
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54 | }
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55 | };
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56 |
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57 | ow(unicorn, ow.object.exactShape({
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58 | rainbow: ow.string,
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59 | stars: {
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60 | value: ow.number
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61 | }
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62 | }));
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63 | //=> ArgumentError: Expected property `stars.value` to be of type `number` but received type `string` in object `unicorn`
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64 | ```
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65 |
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66 | ***Note:*** If you intend on using `ow` for development purposes only, use `require('ow/dev-only')` instead of the usual `import 'ow'`, and run the bundler with `NODE_ENV` set to `production` (e.g. `$ NODE_ENV="production" parcel build index.js`). This will make `ow` automatically export a shim when running in production, which should result in a significantly lower bundle size.
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67 |
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68 | ## API
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69 |
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70 | [Complete API documentation](https://sindresorhus.com/ow/interfaces/ow.html)
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71 |
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72 | Ow includes TypeScript type guards, so using it will narrow the type of previously-unknown values.
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73 |
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74 | ```ts
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75 | function (input: unknown) {
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76 | input.slice(0, 3) // Error, Property 'slice' does not exist on type 'unknown'
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77 |
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78 | ow(input, ow.string)
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79 |
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80 | input.slice(0, 3) // OK
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81 | }
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82 | ```
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83 |
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84 | ### ow(value, predicate)
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85 |
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86 | Test if `value` matches the provided `predicate`. Throws an `ArgumentError` if the test fails.
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87 |
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88 | ### ow(value, label, predicate)
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89 |
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90 | Test if `value` matches the provided `predicate`. Throws an `ArgumentError` with the specified `label` if the test fails.
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91 |
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92 | The `label` is automatically inferred in Node.js but you can override it by passing in a value for `label`. The automatic label inference doesn't work in the browser.
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93 |
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94 | ### ow.isValid(value, predicate)
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95 |
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96 | Returns `true` if the value matches the predicate, otherwise returns `false`.
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97 |
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98 | ### ow.create(predicate)
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99 |
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100 | Create a reusable validator.
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101 |
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102 | ```ts
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103 | const checkPassword = ow.create(ow.string.minLength(6));
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104 |
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105 | const password = 'foo';
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106 |
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107 | checkPassword(password);
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108 | //=> ArgumentError: Expected string `password` to have a minimum length of `6`, got `foo`
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109 | ```
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110 |
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111 | ### ow.create(label, predicate)
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112 |
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113 | Create a reusable validator with a specific `label`.
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114 |
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115 | ```ts
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116 | const checkPassword = ow.create('password', ow.string.minLength(6));
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117 |
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118 | checkPassword('foo');
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119 | //=> ArgumentError: Expected string `password` to have a minimum length of `6`, got `foo`
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120 | ```
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121 |
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122 | ### ow.any(...predicate[])
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123 |
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124 | Returns a predicate that verifies if the value matches at least one of the given predicates.
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125 |
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126 | ```ts
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127 | ow('foo', ow.any(ow.string.maxLength(3), ow.number));
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128 | ```
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129 |
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130 | ### ow.optional.{type}
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131 |
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132 | Makes the predicate optional. An optional predicate means that it doesn't fail if the value is `undefined`.
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133 |
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134 | ```ts
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135 | ow(1, ow.optional.number);
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136 |
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137 | ow(undefined, ow.optional.number);
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138 | ```
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139 |
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140 | ### ow.{type}
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141 |
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142 | All the below types return a predicate. Every predicate has some extra operators that you can use to test the value even more fine-grained.
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143 |
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144 | #### Primitives
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145 |
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146 | - [`undefined`](https://sindresorhus.com/ow/interfaces/ow.html#undefined)
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147 | - [`null`](https://sindresorhus.com/ow/interfaces/ow.html#null)
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148 | - [`string`](https://sindresorhus.com/ow/classes/stringpredicate.html)
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149 | - [`number`](https://sindresorhus.com/ow/classes/numberpredicate.html)
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150 | - [`boolean`](https://sindresorhus.com/ow/classes/booleanpredicate.html)
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151 | - [`symbol`](https://sindresorhus.com/ow/interfaces/ow.html#symbol)
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152 |
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153 | #### Built-in types
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154 |
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155 | - [`array`](https://sindresorhus.com/ow/classes/arraypredicate.html)
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156 | - [`function`](https://sindresorhus.com/ow/interfaces/ow.html#function)
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157 | - [`buffer`](https://sindresorhus.com/ow/interfaces/ow.html#buffer)
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158 | - [`object`](https://sindresorhus.com/ow/classes/objectpredicate.html)
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159 | - [`regExp`](https://sindresorhus.com/ow/interfaces/ow.html#regexp)
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160 | - [`date`](https://sindresorhus.com/ow/classes/datepredicate.html)
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161 | - [`error`](https://sindresorhus.com/ow/classes/errorpredicate.html)
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162 | - [`promise`](https://sindresorhus.com/ow/interfaces/ow.html#promise)
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163 | - [`map`](https://sindresorhus.com/ow/classes/mappredicate.html)
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164 | - [`set`](https://sindresorhus.com/ow/classes/setpredicate.html)
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165 | - [`weakMap`](https://sindresorhus.com/ow/classes/weakmappredicate.html)
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166 | - [`weakSet`](https://sindresorhus.com/ow/classes/weaksetpredicate.html)
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167 |
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168 | #### Typed arrays
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169 |
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170 | - [`int8Array`](https://sindresorhus.com/ow/interfaces/ow.html#int8Array)
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171 | - [`uint8Array`](https://sindresorhus.com/ow/interfaces/ow.html#uint8Array)
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172 | - [`uint8ClampedArray`](https://sindresorhus.com/ow/interfaces/ow.html#uint8ClampedArray)
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173 | - [`int16Array`](https://sindresorhus.com/ow/interfaces/ow.html#int16Array)
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174 | - [`uint16Array`](https://sindresorhus.com/ow/interfaces/ow.html#uint16Array)
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175 | - [`int32Array`](https://sindresorhus.com/ow/interfaces/ow.html#in32Array)
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176 | - [`uint32Array`](https://sindresorhus.com/ow/interfaces/ow.html#uin32Array)
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177 | - [`float32Array`](https://sindresorhus.com/ow/interfaces/ow.html#float32Array)
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178 | - [`float64Array`](https://sindresorhus.com/ow/interfaces/ow.html#float64Array)
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179 |
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180 | #### Structured data
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181 |
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182 | - [`arrayBuffer`](https://sindresorhus.com/ow/interfaces/ow.html#arraybuffer)
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183 | - [`dataView`](https://sindresorhus.com/ow/interfaces/ow.html#dataview)
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184 |
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185 | #### Miscellaneous
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186 |
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187 | - [`nan`](https://sindresorhus.com/ow/interfaces/ow.html#nan)
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188 | - [`nullOrUndefined`](https://sindresorhus.com/ow/interfaces/ow.html#nullorundefined)
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189 | - [`iterable`](https://sindresorhus.com/ow/interfaces/ow.html#iterable)
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190 | - [`typedArray`](https://sindresorhus.com/ow/interfaces/ow.html#typedarray)
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191 |
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192 | ### Predicates
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193 |
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194 | The following predicates are available on every type.
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195 |
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196 | #### not
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197 |
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198 | Inverts the following predicate.
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199 |
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200 | ```ts
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201 | ow(1, ow.number.not.infinite);
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202 |
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203 | ow('', ow.string.not.empty);
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204 | //=> ArgumentError: Expected string to not be empty, got ``
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205 | ```
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206 |
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207 | #### is(fn)
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208 |
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209 | Use a custom validation function. Return `true` if the value matches the validation, return `false` if it doesn't.
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210 |
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211 | ```ts
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212 | ow(1, ow.number.is(x => x < 10));
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213 |
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214 | ow(1, ow.number.is(x => x > 10));
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215 | //=> ArgumentError: Expected `1` to pass custom validation function
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216 | ```
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217 |
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218 | Instead of returning `false`, you can also return a custom error message which results in a failure.
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219 |
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220 | ```ts
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221 | const greaterThan = (max: number, x: number) => {
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222 | return x > max || `Expected \`${x}\` to be greater than \`${max}\``;
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223 | };
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224 |
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225 | ow(5, ow.number.is(x => greaterThan(10, x)));
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226 | //=> ArgumentError: Expected `5` to be greater than `10`
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227 | ```
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228 |
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229 | #### validate(fn)
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230 |
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231 | Use a custom validation object. The difference with `is` is that the function should return a validation object, which allows more flexibility.
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232 |
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233 | ```ts
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234 | ow(1, ow.number.validate(value => ({
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235 | validator: value > 10,
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236 | message: `Expected value to be greater than 10, got ${value}`
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237 | })));
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238 | //=> ArgumentError: (number) Expected value to be greater than 10, got 1
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239 | ```
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240 |
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241 | You can also pass in a function as `message` value which accepts the label as argument.
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242 |
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243 | ```ts
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244 | ow(1, 'input', ow.number.validate(value => ({
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245 | validator: value > 10,
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246 | message: label => `Expected ${label} to be greater than 10, got ${value}`
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247 | })));
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248 | //=> ArgumentError: Expected number `input` to be greater than 10, got 1
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249 | ```
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250 |
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251 | #### message(string | fn)
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252 |
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253 | Provide a custom message:
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254 |
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255 | ```ts
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256 | ow('🌈', 'unicorn', ow.string.equals('🦄').message('Expected unicorn, got rainbow'));
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257 | //=> ArgumentError: Expected unicorn, got rainbow
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258 | ```
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259 |
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260 | You can also pass in a function which receives the value as the first parameter and the label as the second parameter and is expected to return the message.
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261 |
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262 | ```ts
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263 | ow('🌈', ow.string.minLength(5).message((value, label) => `Expected ${label}, to have a minimum length of 5, got \`${value}\``));
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264 | //=> ArgumentError: Expected string, to be have a minimum length of 5, got `🌈`
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265 | ```
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266 |
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267 | It's also possible to add a separate message per validation:
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268 |
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269 | ```ts
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270 | ow(
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271 | '1234',
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272 | ow.string
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273 | .minLength(5).message((value, label) => `Expected ${label}, to be have a minimum length of 5, got \`${value}\``)
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274 | .url.message('This is no url')
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275 | );
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276 | //=> ArgumentError: Expected string, to be have a minimum length of 5, got `1234`
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277 |
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278 | ow(
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279 | '12345',
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280 | ow.string
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281 | .minLength(5).message((value, label) => `Expected ${label}, to be have a minimum length of 5, got \`${value}\``)
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282 | .url.message('This is no url')
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283 | );
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284 | //=> ArgumentError: This is no url
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285 | ```
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286 |
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287 | This can be useful for creating your own reusable validators which can be extracted to a separate npm package.
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288 |
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289 | ## Maintainers
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290 |
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291 | - [Sindre Sorhus](https://github.com/sindresorhus)
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292 | - [Sam Verschueren](https://github.com/SamVerschueren)
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293 |
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294 | ## Related
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295 |
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296 | - [@sindresorhus/is](https://github.com/sindresorhus/is) - Type check values
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297 | - [ngx-ow](https://github.com/SamVerschueren/ngx-ow) - Angular form validation on steroids
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