49 lines
1.8 KiB
Markdown
49 lines
1.8 KiB
Markdown
## Operators and Aliases
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Because the `==` operator frequently causes undesirable coercion, is intransitive, and has a different meaning than in other languages, CoffeeScript compiles `==` into `===`, and `!=` into `!==`. In addition, `is` compiles into `===`, and `isnt` into `!==`.
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You can use `not` as an alias for `!`.
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For logic, `and` compiles to `&&`, and `or` into `||`.
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Instead of a newline or semicolon, `then` can be used to separate conditions from expressions, in `while`, `if`/`else`, and `switch`/`when` statements.
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As in [YAML](http://yaml.org/), `on` and `yes` are the same as boolean `true`, while `off` and `no` are boolean `false`.
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`unless` can be used as the inverse of `if`.
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As a shortcut for `this.property`, you can use `@property`.
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You can use `in` to test for array presence, and `of` to test for JavaScript object-key presence.
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In a `for` loop, `from` compiles to the [ES2015 `of`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of). (Yes, it’s unfortunate; the CoffeeScript `of` predates the ES2015 `of`.)
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To simplify math expressions, `**` can be used for exponentiation and `//` performs integer division. `%` works just like in JavaScript, while `%%` provides [“dividend dependent modulo”](https://en.wikipedia.org/wiki/Modulo_operation):
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```
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codeFor('modulo')
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```
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All together now:
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| CoffeeScript | JavaScript |
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| --- | --- |
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| `is` | `===` |
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| `isnt` | `!==` |
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| `not` | `!` |
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| `and` | `&&` |
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| `or` | `||` |
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| `true`, `yes`, `on` | `true` |
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| `false`, `no`, `off`  | `false` |
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| `@`, `this` | `this` |
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| `a in b` | `[].indexOf.call(b, a) >= 0` |
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| `a of b` | `a in b` |
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| `for a from b` | `for (a of b)` |
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| `a ** b` | `Math.pow(a, b)` |
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| `a // b` | `Math.floor(a / b)` |
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| `a %% b` | `(a % b + b) % b` |
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```
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codeFor('aliases')
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```
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