Compare calling Function() once-per-function vs first concatenating source text into an array of functions

function-constructor-base-cost.js

{

function empty () {}

const fnsLength = 10;
const fns = new Array(fnsLength).fill(empty);

const fnStrings = fns.map(x => x.toString());

var ix = 0;

function emptySingle () {
    return fns.map(_ => Function(`'use strict';return (function () {}); //${ix++}`)());
}

function uncached () {
    return fns.map(x => Function(`'use strict';return (${x.toString()}); //${ix++}`)());
}

var strs;
function cached () {
    return fnStrings.map(x => Function(`'use strict';return (${x}); //${ix++}`)());
}

function arrayTogether () {
    const fnStrings = fns.map(x => x.toString());
    const fnArray = `'use strict';return [(${fnStrings.join('),(')})]; //${ix++}`;
    return Function(fnArray)();
}

function emptyTogether () {
    const fnStrings = fns.map(x => "(function () {})");
    const fnArray = `'use strict';return [${fnStrings.join(',')}]; //${ix++}`;
    return Function(fnArray)();
}


const o = {};
const ITERATIONS = 1e2;
function runFn(fn) {
    var i=ITERATIONS;
    var start = new Date();
    while (i--) {
        const genFns = fn();
        for (const genFn of genFns) {
            genFn();
        }
    }
    var dur = new Date() - start;
    var numFns = fns.length*ITERATIONS;
    console.log(fn.name + " " + dur + "ms / " + (dur * 1000 / numFns) + " us each / " + numFns + " fns");
}


runFn(emptyTogether);
runFn(arrayTogether);
runFn(emptySingle);
runFn(cached);
runFn(uncached);

}