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?

Accepted Answer

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.

What means Javascript comma separated functions

Solution

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