The Array constructor

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The prototype



How this works

Closures and references

The arguments object

Scopes and namespaces


Equality and comparisons


The Array constructor

The for in loop

The typeof operator

The instanceof operator

Type casting

undefined and null

Reasons against eval

setTimeout and setInterval

Automatic semicolon insertion

The Array constructor

Since the Array constructor is ambiguous in how it deals with its parameters, it is highly recommended to always use the array literals - [] notation - when creating new arrays.

[1, 2, 3]; // Result: [1, 2, 3]
new Array(1, 2, 3); // Result: [1, 2, 3]
[3]; // Result: [3]
new Array(3); // Result: []
new Array('3') // Result: ['3']

In cases when there is only one argument passed to the Array constructor, and that argument is a Number, the constructor will return a new sparse array with thelength property set to the value of the argument. It should be noted that only the length property of the new array will be set this way, the actual indexes of the array will not be initialized.

var arr = new Array(3);
arr[1]; // undefined
1 in arr; // false, the index was not set

The behavior of being able to set the length of the array upfront only comes in handy in a few cases, like repeating a string, in which it avoids the use of a for loopcode.

new Array(count + 1).join(stringToRepeat);

In conclusion

The use of the Array constructor should be avoided as much as possible. Literals are definitely preferred. They are shorter and have a clearer syntax; therefore, they also increase the readability of the code.

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