What means Javascript comma separated functions

Question

I am reading a javscript dojo library and I see many complex functions which I can't understand. For example:

_refreshUI: function () {
    this._hasUI && (g.empty(this.flowContainer), f.forEach(this.basemaps, function (a, b) { a.id || (a.id = "basemap_" + b); this.flowContainer.appendChild(this._buildNodeLayout(a))
}, this), g.create("br", { style: { clear: "both" } }, this.flowContainer), this._markSelected(this._selectedBasemap))

this function is written on a single line. It contains functions separated with commas. So I can not read it.

I do not ask what the above function does.

What does this mean?:

this._hasUI && (firstFunction, secondFunction, ...)

What does it do? Or how can I write it clearly?

Answer 1

This is a way of only executing the functions if this._hasUI resolves to true.

Try this:

true && (console.log(1), console.log(2));

And this:

false && (console.log(1), console.log(2));

You'll see that only the first line will run the console.log() functions.

This is because the boolean AND operator (&&) is evaluated lazily. If the left side of the operator resolves to false, the interpreter won't bother evaluating the right side, because the operation can never result in true. This means the functions on the right will only be executed if the left side is a truthy value.