1 | # @babel/plugin-check-constants
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2 |
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3 | > Validate ES2015 constants (prevents reassignment of const variables).
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4 |
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5 | ## Example
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6 |
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7 | **In**
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8 |
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9 | ```js
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10 | const a = 1;
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11 | a = 2;
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12 | ```
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13 |
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14 | **Out**
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15 |
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16 | ```bash
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17 | repl: "a" is read-only
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18 | 1 | const a = 1;
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19 | > 2 | a = 2;
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20 | | ^
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21 | ```
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22 |
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23 |
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24 | ## Installation
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25 |
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26 | ```sh
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27 | npm install --save-dev @babel/plugin-check-constants
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28 | ```
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29 |
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30 | ## Usage
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31 |
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32 | ### Via `.babelrc` (Recommended)
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33 |
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34 | **.babelrc**
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35 |
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36 | ```json
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37 | {
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38 | "plugins": ["@babel/check-constants"]
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39 | }
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40 | ```
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41 |
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42 | ### Via CLI
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43 |
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44 | ```sh
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45 | babel --plugins @babel/check-constants script.js
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46 | ```
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47 |
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48 | ### Via Node API
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49 |
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50 | ```javascript
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51 | require("@babel/core").transform("code", {
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52 | plugins: ["@babel/check-constants"]
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53 | });
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54 | ```
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55 |
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56 | ## Note
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57 |
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58 | This check will only validate consts. If you need it to compile down to `var` then you must also install and enable [`@babel/plugin-transform-block-scoping`](http://babeljs.io/docs/plugins/transform-block-scoping/).
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