Useful JavaScript Patterns

Generate a random integer from m to n

JavaScript has no direct function for generating a number within a range. Math.random() returns a pseudorandom floating-point number from 0 up to, but not including, 1. It can be used to generate an integer in any range:

function getRandom(floor, ceil) {
    return parseInt(Math.random() * (ceil - floor + 1) + floor)
}

Warn before closing a tab

Bind the beforeunload event. Its return value has a special purpose: preventing users from accidentally closing a page and losing edits. There is no need to call confirm; return the warning text instead:

window.onbeforeunload = function () {
    return "Your changes have not been saved";
};

The warning would also appear during a form submission, when it is unnecessary. Clear the handler in the form’s submit function:

window.onbeforeunload = null;

Construct an object with a closure

For the same get_name() method, the closure pattern is faster.

Prototype pattern:

var X = function(name){ this.name = name; }
X.prototype.get_name = function() { return this.name; };

Closure pattern:

var Y = function(name) {
    var y = { name: name };
    return { 'get_name': function() { return y.name; } };
};

Originally published on SegmentFault.