In the following javascript code there is [] being assigned as the value of a variable, what does it mean?
var openTollDebug = [];
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8 Answers
it is an array literal. It is not quite the same as declaring new Array() - the Array object can be overwritten in JavaScript, but the array literal can't. Here's an example to demonstrate
// let's overwrite the Array object
Array = function(id) {
this.id = id;
}
var a = new Array(1);
var b = [];
console.log(a.hasOwnProperty("id")); // true
console.log(b.hasOwnProperty("id")); // false
console.log(a.push); // false, push doesn't exist on a
console.log(b.push); // true, but it does on b
b.push(2);
console.log(b); // outputs [2]
4 Comments
Tim Down
So long as
Array hasn't been overwritten, new Array() and [] are functionally identical.
Russ Cam
@Tim - yes they are. There is also a difference in intializing values and length -
new Array(5) is not the same as [5] :)Russ Cam
for the person who gave the -1 : why? I believe I qualified that declaring
[] and new Array() is not quite the same as the latter is based on the condition that Array has not been overwritten.
Pacerier
@RussCam, So how do we override
[] constructor?It means an array.
var openTollDebug = [];
declares the openTollDebug variable and initializes it to an empty array. To put elements into the array you could do the following:
var stringArray = ['element1', 'element2', 'element3'];
alert(stringArray[1]); // displays 'element2'
var numberArray = [1, 2, 3, 4];
alert(numberArray[2]); // displays 3
var objectArray = [{ name: 'john' }, { name: 'peter' }, { name: 'tom' }];
alert(objectArray[1].name); // displays 'peter'
Comments
It's an empty array, and is equal to
var openTollDebug = new Array();
Comments
It is shorthand for empty array. Same as new Array(). Also {} is an empty object. Objects are like hashtables in Js so you can use it as a dictionary.
Comments
It creates an empty array.
This is a good way to have a non-null object.
In JavaScript, it is then very easy to add functions and properties to that object. For example:
openTollDebug.title = 'hello world';
openTollDebug.show = function(){alert('Debug');};
As an array, you can add items:
openTollDebug.push('added item');
openTollDebug[3] = 'just add anywhere';
Comments
Many languages have constructs for literals. The [] is an Array literal.
var openTollDebug = [];
is the same as
var openTollDebug = new Array();
Just know that using [] preferred for performance reasons.
There are other literals like Object literals
var MyObject = {
name:'default',
age:22,
hobbies:["golf","video games","otherstuff"]
}
Notice the array literal with data. The [] creates an empty array.
Comments
Try to use literals due to performance. You dont write
var obj = new Object({name: 'John'})
You just write
var obj = {name: 'John'}
You also dont write
button.onclick = new Function("alert('Clicked!')");
You write
button.onclick = function () { alert('Clicked') }
And here's a link to a nice blog post about it
Comments
var b = [] //it is an array literal.
1 Comment
Quaternion
You should check to see if there are answers which already provide the same information.