80 lines
2.0 KiB
Markdown
80 lines
2.0 KiB
Markdown
|
---
|
||
|
|
id: cf1111c1c11feddfaeb5bdef
|
||
|
|
title: Iterate with JavaScript For Loops
|
||
|
|
challengeType: 1
|
||
|
|
videoUrl: 'https://scrimba.com/c/c9yNVCe'
|
||
|
|
forumTopicId: 18219
|
||
|
|
dashedName: iterate-with-javascript-for-loops
|
||
|
|
---
|
||
|
|
|
||
|
|
# --description--
|
||
|
|
|
||
|
|
You can run the same code multiple times by using a loop.
|
||
|
|
|
||
|
|
The most common type of JavaScript loop is called a `for` loop because it runs "for" a specific number of times.
|
||
|
|
|
||
|
|
For loops are declared with three optional expressions separated by semicolons:
|
||
|
|
|
||
|
|
`for ([initialization]; [condition]; [final-expression])`
|
||
|
|
|
||
|
|
The `initialization` statement is executed one time only before the loop starts. It is typically used to define and setup your loop variable.
|
||
|
|
|
||
|
|
The `condition` statement is evaluated at the beginning of every loop iteration and will continue as long as it evaluates to `true`. When `condition` is `false` at the start of the iteration, the loop will stop executing. This means if `condition` starts as `false`, your loop will never execute.
|
||
|
|
|
||
|
|
The `final-expression` is executed at the end of each loop iteration, prior to the next `condition` check and is usually used to increment or decrement your loop counter.
|
||
|
|
|
||
|
|
In the following example we initialize with `i = 0` and iterate while our condition `i < 5` is true. We'll increment `i` by `1` in each loop iteration with `i++` as our `final-expression`.
|
||
|
|
|
||
|
|
```js
|
||
|
|
var ourArray = [];
|
||
|
|
for (var i = 0; i < 5; i++) {
|
||
|
|
ourArray.push(i);
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
`ourArray` will now contain `[0,1,2,3,4]`.
|
||
|
|
|
||
|
|
# --instructions--
|
||
|
|
|
||
|
|
Use a `for` loop to work to push the values 1 through 5 onto `myArray`.
|
||
|
|
|
||
|
|
# --hints--
|
||
|
|
|
||
|
|
You should be using a `for` loop for this.
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert(/for\s*\([^)]+?\)/.test(code));
|
||
|
|
```
|
||
|
|
|
||
|
|
`myArray` should equal `[1,2,3,4,5]`.
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert.deepEqual(myArray, [1, 2, 3, 4, 5]);
|
||
|
|
```
|
||
|
|
|
||
|
|
# --seed--
|
||
|
|
|
||
|
|
## --after-user-code--
|
||
|
|
|
||
|
|
```js
|
||
|
|
if (typeof myArray !== "undefined"){(function(){return myArray;})();}
|
||
|
|
```
|
||
|
|
|
||
|
|
## --seed-contents--
|
||
|
|
|
||
|
|
```js
|
||
|
|
// Setup
|
||
|
|
var myArray = [];
|
||
|
|
|
||
|
|
// Only change code below this line
|
||
|
|
```
|
||
|
|
|
||
|
|
# --solutions--
|
||
|
|
|
||
|
|
```js
|
||
|
|
var myArray = [];
|
||
|
|
for (var i = 1; i < 6; i++) {
|
||
|
|
myArray.push(i);
|
||
|
|
}
|
||
|
|
```
|