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.

Created with the Personal Edition of HelpNDoc: Create iPhone web-based documentation

Intro	Objects	The prototype
hasOwnProperty	Functions	How this works
Closures and references	The arguments object	Scopes and namespaces
Constructors	Equality and comparisons	Arrays
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