Question

What the proper name of this Javascript pattern where a variable is assigned to value of a return function?

// array with a ton of random values. 
var once = (function(){

        var i = 10000, arr = [];

        while(i){
            arr.push( Math.random() * i );
            i--;
        }
        arr = arr.toString(); 

        return (function(){
            return arr;
        }());

}());

Edit – a better example:

 var once = (function(){

    // Only run a really expensive operation once...
    var i = 10000, arr = [], x;

    while(i){
        arr.push( Math.random() * i );
        i--;
    }
    arr = arr.toString(); 
    x = parseFloat(arr.toString());

    // then return the result of another function
    return function(){
        return x * (Math.random() * 10);
    };

}());

$(window).resize(function(){
    console.info(once());
});

Answer 1

I believe you’re looking for memoization.

In computing, memoization is an optimization technique used primarily to speed up computer programs by having function calls avoid repeating the calculation of results for previously processed inputs.

…

A memoized function “remembers” the results corresponding to some set of specific inputs. Subsequent calls with remembered inputs return the remembered result rather than recalculating it, thus eliminating the primary cost of a call with given parameters from all but the first call made to the function with those parameters.