# babel-plugin-transform-do-expressions
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> Compile `do` expressions to ES5
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## Detail
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> The `do { .. }` expression executes a block (with one or many statements in it), and the final statement completion value inside the block becomes the completion value of the do expression.
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from [You Don't Know JS](https://github.com/getify/You-Dont-Know-JS/blob/master/types%20%26%20grammar/ch5.md#statement-completion-values)
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It can be seen as a complex version of the [ternary operator](http://mdn.io/ternary):
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```js
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let a = do {
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if(x > 10) {
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'big';
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} else {
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'small';
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}
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};
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// is equivalent to:
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let a = x > 10 ? 'big' : 'small';
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```
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[Try in REPL](http://babeljs.io/repl/#?evaluate=true&presets=es2015%2Cstage-0&code=%0Alet%20x%20%3D%20100%3B%0A%0Alet%20a%20%3D%20do%20%7B%0A%20%20if(x%20%3E%2010)%20%7B%0A%20%20%20%20'big'%3B%0A%20%20%7D%20else%20%7B%0A%20%20%20%20'small'%3B%0A%20%20%7D%0A%7D%3B%0A%0Aconsole.log(a)%3B)
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This example is not the best usage because it is too simple and using a ternary operator is a better option but you can have a much more complex condition in the `do { ... }` expression with several `if ... else` chains:
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```js
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let x = 100;
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let y = 20;
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let a = do {
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if(x > 10) {
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if(y > 20) {
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'big x, big y';
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} else {
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'big x, small y';
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}
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} else {
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if(y > 10) {
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'small x, big y';
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} else {
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'small x, small y';
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}
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}
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};
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```
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[Try in REPL](http://babeljs.io/repl/#?evaluate=true&presets=es2015%2Cstage-0&code=let%20x%20%3D%20100%3B%0Alet%20y%20%3D%2020%3B%0A%0Alet%20a%20%3D%20do%20%7B%0A%20%20if(x%20%3E%2010)%20%7B%0A%20%20%20%20if(y%20%3E%2020)%20%7B%0A%20%20%20%20%20%20'big%20x%2C%20big%20y'%3B%0A%20%20%20%20%7D%20else%20%7B%0A%20%20%20%20%20%20'big%20x%2C%20small%20y'%3B%0A%20%20%20%20%7D%0A%20%20%7D%20else%20%7B%0A%20%20%20%20if(y%20%3E%2010)%20%7B%0A%20%20%20%20%20%20'small%20x%2C%20big%20y'%3B%0A%20%20%20%20%7D%20else%20%7B%0A%20%20%20%20%20%20'small%20x%2C%20small%20y'%3B%0A%20%20%20%20%7D%0A%20%20%7D%0A%7D%3B%0A%0Aconsole.log(a)%3B)
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## Example
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### In JSX
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One of the most useful usage of the `do` expression is inside JSX. If we want to conditionally display a component we usually have to call another function which would implement the condition and return the correct value, for example:
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```js
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const getColoredComponent = color => {
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if(color === 'blue') { return <BlueComponent/>; }
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if(color === 'red') { return <RedComponent/>; }
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if(color === 'green') { return <GreenComponent/>; }
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}
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const Component = props =>
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<div className='myComponent'>
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{getColoredComponent()}
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</div>
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;
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```
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Using a do expression you can add logic inside JSX:
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```js
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const Component = props =>
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<div className='myComponent'>
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{do {
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if(color === 'blue') { <BlueComponent/>; }
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if(color === 'red') { <RedComponent/>; }
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if(color === 'green') { <GreenComponent/>; }
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}}
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</div>
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;
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```
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[Try in REPL](http://babeljs.io/repl/#?evaluate=true&presets=es2015%2Creact%2Cstage-0&code=const%20Component%20%3D%20props%20%3D%3E%0A%20%20%3Cdiv%20className%3D'myComponent'%3E%0A%20%20%20%20%7Bdo%20%7B%0A%20%20%20%20%20%20if(color%20%3D%3D%3D%20'blue')%20%7B%20%3CBlueComponent%2F%3E%3B%20%7D%0A%20%20%20%20%20%20if(color%20%3D%3D%3D%20'red')%20%7B%20%3CRedComponent%2F%3E%3B%20%7D%0A%20%20%20%20%20%20if(color%20%3D%3D%3D%20'green')%20%7B%20%3CGreenComponent%2F%3E%3B%20%7D%0A%20%20%20%20%7D%7D%0A%20%20%3C%2Fdiv%3E%0A%3B)
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## Installation
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```sh
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npm install --save-dev babel-plugin-transform-do-expressions
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```
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## Usage
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### Via `.babelrc` (Recommended)
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**.babelrc**
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```json
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{
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"plugins": ["transform-do-expressions"]
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}
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```
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### Via CLI
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```sh
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babel --plugins transform-do-expressions script.js
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```
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### Via Node API
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```javascript
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require("babel-core").transform("code", {
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plugins: ["transform-do-expressions"]
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});
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```
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## References
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- [Proposal](http://wiki.ecmascript.org/doku.php?id=strawman:do_expressions)
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- [You Don't Know JS](https://github.com/getify/You-Dont-Know-JS/blob/master/types%20%26%20grammar/ch5.md#statement-completion-values)
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- Very handy for conditions inside JSX: [reactjs/react-future#35](https://github.com/reactjs/react-future/issues/35#issuecomment-120009203)
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