103 lines
2.6 KiB
Markdown
103 lines
2.6 KiB
Markdown
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---
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id: 587d7b7b367417b2b2512b13
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title: Copy an Array with the Spread Operator
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challengeType: 1
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forumTopicId: 301157
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dashedName: copy-an-array-with-the-spread-operator
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---
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# --description--
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While `slice()` allows us to be selective about what elements of an array to copy, among several other useful tasks, ES6's new <dfn>spread operator</dfn> allows us to easily copy *all* of an array's elements, in order, with a simple and highly readable syntax. The spread syntax simply looks like this: `...`
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In practice, we can use the spread operator to copy an array like so:
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```js
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let thisArray = [true, true, undefined, false, null];
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let thatArray = [...thisArray];
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// thatArray equals [true, true, undefined, false, null]
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// thisArray remains unchanged and thatArray contains the same elements as thisArray
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```
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# --instructions--
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We have defined a function, `copyMachine` which takes `arr` (an array) and `num` (a number) as arguments. The function is supposed to return a new array made up of `num` copies of `arr`. We have done most of the work for you, but it doesn't work quite right yet. Modify the function using spread syntax so that it works correctly (hint: another method we have already covered might come in handy here!).
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# --hints--
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`copyMachine([true, false, true], 2)` should return `[[true, false, true], [true, false, true]]`
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```js
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assert.deepEqual(copyMachine([true, false, true], 2), [
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[true, false, true],
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[true, false, true]
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]);
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```
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`copyMachine([1, 2, 3], 5)` should return `[[1, 2, 3], [1, 2, 3], [1, 2, 3], [1, 2, 3], [1, 2, 3]]`
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```js
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assert.deepEqual(copyMachine([1, 2, 3], 5), [
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[1, 2, 3],
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[1, 2, 3],
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[1, 2, 3],
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[1, 2, 3],
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[1, 2, 3]
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]);
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```
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`copyMachine([true, true, null], 1)` should return `[[true, true, null]]`
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```js
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assert.deepEqual(copyMachine([true, true, null], 1), [[true, true, null]]);
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```
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`copyMachine(["it works"], 3)` should return `[["it works"], ["it works"], ["it works"]]`
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```js
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assert.deepEqual(copyMachine(['it works'], 3), [
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['it works'],
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['it works'],
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['it works']
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]);
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```
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The `copyMachine` function should utilize the `spread operator` with array `arr`
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```js
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assert(__helpers.removeJSComments(code).match(/\.\.\.arr/));
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```
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# --seed--
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## --seed-contents--
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```js
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function copyMachine(arr, num) {
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let newArr = [];
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while (num >= 1) {
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// Only change code below this line
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// Only change code above this line
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num--;
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}
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return newArr;
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}
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console.log(copyMachine([true, false, true], 2));
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```
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# --solutions--
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```js
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function copyMachine(arr,num){
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let newArr=[];
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while(num >=1){
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newArr.push([...arr]);
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num--;
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}
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return newArr;
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}
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console.log(copyMachine([true, false, true], 2));
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```
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