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37 lines
731 B
Markdown
37 lines
731 B
Markdown
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---
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id: 4cd0d42b-3414-4402-95f1-7498fbc52c20
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title: JavaScript In Operator
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---
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# Description
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`in`[^1] tells us if indices inside an [array](20200826201029-arrays) or
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[object](20200826201605-objects) have no associated element.
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# Syntax
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``` javascript
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const arr = ['a',,'b']
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console.log(0 in arr) // true
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console.log(1 in arr) // false
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console.log(2 in arr) // true
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console.log(arr[1]) // undefined
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```
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``` javascript
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const car = { make: "Honda", model: "Accord", year: 1998 };
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console.log("make" in car); // true
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delete car.make;
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if ("make" in car === false) {
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car.make = "Suzuki";
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}
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console.log(car.make); //Suzuki
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```
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# Footnotes
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[^1]: <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/in>
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