JavaScript - run once without booleans

Question

Is there a way to run a piece of JavaScript code only ONCE, without using boolean flag variables to remember whether it has already been ran or not?

Spe

Answer 1

A problem with quite a few of these approaches is that they depend on function names to work: Mike's approach will fail if you create a function with "x = function() ..." and Lekensteyn's approach will fail if you set x = useThisFunctionOnce before useThisFunctionOnce is called.

I would recommend using Russ's closure approach if you want it run right away or the approach taken by Underscore.js if you want to delay execution:

function once(func) {
    var ran = false, memo;
    return function() {
        if (ran) return memo;
        ran = true;
        return memo = func.apply(this, arguments);
    };
}

var myFunction = once(function() {
    return new Date().toString();
});

setInterval(function() {console.log(myFunction());}, 1000);

On the first execution, the inner function is executed and the results are returned. On subsequent runs, the original result object is returned.