94 lines
2.7 KiB
Markdown
94 lines
2.7 KiB
Markdown
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---
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id: 587d7b7b367417b2b2512b14
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title: Check For The Presence of an Element With indexOf()
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challengeType: 1
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forumTopicId: 301154
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dashedName: check-for-the-presence-of-an-element-with-indexof
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---
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# --description--
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Since arrays can be changed, or *mutated*, at any time, there's no guarantee about where a particular piece of data will be on a given array, or if that element even still exists. Luckily, JavaScript provides us with another built-in method, `indexOf()`, that allows us to quickly and easily check for the presence of an element on an array. `indexOf()` takes an element as a parameter, and when called, it returns the position, or index, of that element, or `-1` if the element does not exist on the array.
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For example:
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```js
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let fruits = ['apples', 'pears', 'oranges', 'peaches', 'pears'];
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fruits.indexOf('dates');
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fruits.indexOf('oranges');
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fruits.indexOf('pears');
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```
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`indexOf('dates')` returns `-1`, `indexOf('oranges')` returns `2`, and `indexOf('pears')` returns `1` (the first index at which each element exists).
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# --instructions--
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`indexOf()` can be incredibly useful for quickly checking for the presence of an element on an array. We have defined a function, `quickCheck`, that takes an array and an element as arguments. Modify the function using `indexOf()` so that it returns `true` if the passed element exists on the array, and `false` if it does not.
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# --hints--
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The `quickCheck` function should return a boolean (`true` or `false`), not a string (`"true"` or `"false"`)
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```js
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assert.isBoolean(quickCheck(['squash', 'onions', 'shallots'], 'mushrooms'));
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```
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`quickCheck(["squash", "onions", "shallots"], "mushrooms")` should return `false`
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```js
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assert.strictEqual(
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quickCheck(['squash', 'onions', 'shallots'], 'mushrooms'),
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false
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);
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```
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`quickCheck(["onions", "squash", "shallots"], "onions")` should return `true`
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```js
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assert.strictEqual(
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quickCheck(['onions', 'squash', 'shallots'], 'onions'),
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true
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);
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```
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`quickCheck([3, 5, 9, 125, 45, 2], 125)` should return `true`
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```js
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assert.strictEqual(quickCheck([3, 5, 9, 125, 45, 2], 125), true);
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```
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`quickCheck([true, false, false], undefined)` should return `false`
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```js
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assert.strictEqual(quickCheck([true, false, false], undefined), false);
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```
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The `quickCheck` function should utilize the `indexOf()` method
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```js
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assert.notStrictEqual(quickCheck.toString().search(/\.indexOf\(/), -1);
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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 quickCheck(arr, elem) {
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// Only change code below this line
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// Only change code above this line
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}
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console.log(quickCheck(['squash', 'onions', 'shallots'], 'mushrooms'));
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```
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# --solutions--
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```js
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function quickCheck(arr, elem) {
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return arr.indexOf(elem) >= 0;
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}
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```
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