This is an extensive overview of the jQuery.each() function — one of jQuery’s most important and most used functions. In this article, we’ll find out why and take a look at how you can use it.
What is jQuery.each()
jQuery’s each() function is used to loop through each element of the target jQuery object — an object that contains one or more DOM elements, and exposes all jQuery functions. It’s very useful for multi-element DOM manipulation, as well as iterating over arbitrary arrays and object properties.
In addition to this function, jQuery provides a helper function with the same name that can be called without having previously selected or created any DOM elements.
jQuery.each() Syntax
Let’s see the different modes in action.
The following example selects every <div> element on a web page and outputs the index and the ID of each of them:
// DOM ELEMENTS
$('div').each(function(index, value) {
console.log(`div${index}: ${this.id}`);
});
A possible output would be:
div0:header
div1:main
div2:footer
This version uses jQuery’s $(selector).each() function, as opposed to the utility function.
The next example shows the use of the utility function. In this case the object to loop over is given as the first argument. In this example, we'll show how to loop over an array:
// ARRAYS
const arr = [
'one',
'two',
'three',
'four',
'five'
];
$.each(arr, function(index, value) {
console.log(value);
// Will stop running after "three"
return (value !== 'three');
});
// Outputs: one two three
In the last example, we want to demonstrate how to iterate over the properties of an object:
// OBJECTS
const obj = {
one: 1,
two: 2,
three: 3,
four: 4,
five: 5
};
$.each(obj, function(key, value) {
console.log(value);
});
// Outputs: 1 2 3 4 5
This all boils down to providing a proper callback. The callback’s context, this, will be equal to its second argument, which is the current value. However, since the context will always be an object, primitive values have to be wrapped:
$.each({ one: 1, two: 2 } , function(key, value) {
console.log(this);
});
// Number { 1 }
// Number { 2 }
`
This means that there's no strict equality between the value and the context.
$.each({ one: 1 } , function(key, value) {
console.log(this == value);
console.log(this === value);
});
// true
// false
`
The first argument is the current index, which is either a number (for arrays) or string (for objects).
1. Basic jQuery.each() Function Example
Let’s see how the jQuery.each() function helps us in conjunction with a jQuery object. The first example selects all the a elements in the page and outputs their href attribute:
$('a').each(function(index, value){
console.log(this.href);
});
The second example outputs every external href on the web page (assuming the HTTP(S) protocol only):
$('a').each(function(index, value){
const link = this.href;
if (link.match(/https?:\/\//)) {
console.log(link);
}
});
Let’s say we had the following links on the page:
<a href="https://www.sitepoint.com/">SitePoint</a>
<a href="https://developer.mozilla.org">MDN web docs</a>
<a href="http://example.com/">Example Domain</a>
The second example would output:
https://www.sitepoint.com/
https://developer.mozilla.org/
http://example.com/
We should note that DOM elements from a jQuery object are in their "native" form inside the callback passed to jQuery.each(). The reason is that jQuery is in fact just a wrapper around an array of DOM elements. By using jQuery.each(), this array is iterated in the same way as an ordinary array would be. Therefore, we don’t get wrapped elements out of the box.
With reference to our second example, this means we can get an element's href attribute by writing this.href. If we wanted to use jQuery's attr() method, we would need to re-wrap the element like so: $(this).attr('href').
The post 5 jQuery.each() Function Examples appeared first on SitePoint.
by Florian Rappl via SitePoint
