Question

Is there a function in JavaScript similar to Python’s range()?

I think there should be a better way than to write the following lines every time:

array = new Array();
for (i = 0; i < specified_len; i++) {
    array[i] = i;
}

Answer 1

No, there is none, but you can make one.

JavaScript’s implementation of Python’s range()

Trying to emulate how it works in Python, I would create function similar to this:

function range(start, stop, step) {
    if (typeof stop == 'undefined') {
        // one param defined
        stop = start;
        start = 0;
    }

    if (typeof step == 'undefined') {
        step = 1;
    }

    if ((step > 0 && start >= stop) || (step < 0 && start <= stop)) {
        return [];
    }

    var result = [];
    for (var i = start; step > 0 ? i < stop : i > stop; i += step) {
        result.push(i);
    }

    return result;
};

See this jsfiddle for a proof.

Comparison between range() in JavaScript and Python

It works in the following way:

• range(4) returns [0, 1, 2, 3],
• range(3,6) returns [3, 4, 5],
• range(0,10,2) returns [0, 2, 4, 6, 8],
• range(10,0,-1) returns [10, 9, 8, 7, 6, 5, 4, 3, 2, 1],
• range(8,2,-2) returns [8, 6, 4],
• range(8,2) returns [],
• range(8,2,2) returns [],
• range(1,5,-1) returns [],
• range(1,5,-2) returns [],

and its Python counterpart works exactly the same way (at least in the mentioned cases):

>>> range(4)
[0, 1, 2, 3]
>>> range(3,6)
[3, 4, 5]
>>> range(0,10,2)
[0, 2, 4, 6, 8]
>>> range(10,0,-1)
[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
>>> range(8,2,-2)
[8, 6, 4]
>>> range(8,2)
[]
>>> range(8,2,2)
[]
>>> range(1,5,-1)
[]
>>> range(1,5,-2)
[]

So if you need a function to work similarly to Python’s range(), you can use above mentioned solution.