JavaScript, unknown syntax

Question

I'm using the library handsontable and I'd like to get my application running in IE8-IE9 (even though it's not IE < 10 compatible...). When my code use the minify version I get an error in the JS console : "';' expected".

Here is the code.

, {
    get DEFAULT_WIDTH() {
        return 50;
    }
}

I just don't know this syntax. What does "get DEFAULT_WIDTH()" do ?

This function return 50. Perhaps the programmer created this function to avoid use magical numbers. — Sapikelio, Jul 29 '15 at 07:36
well I'm not sure but I think return an int with the value 50 :-) Like Sapikelio said, a default number — Cageman, Jul 29 '15 at 07:37
it's a getter/setter family. check http://stackoverflow.com/questions/1077106/javascript-getters-setters-in-ie — Matteo Rubini, Jul 29 '15 at 07:38
Ypu are geting error in ie 8/9 ? IE of lower version, very sensetive to ";" — Alex Nikulin, Jul 29 '15 at 07:38
Is your question answered? If so, please check the answer that helped you most to understand the topic.If not, let us know what is missing for you. — connexo, Jul 29 '15 at 09:44

Simon Groenewolt · Answer 1 · 2015-07-29T07:43:50.667

1

MDN has documentation for get, including a list of supporting browsers. What get does is invoke a function when the property is looked up. See Defining getters and setters for a more general explanation.

edited Jul 29 '15 at 07:43

answered Jul 29 '15 at 07:39

Simon Groenewolt

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probably easier to read the [high level definition](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Working_with_Objects#Defining_getters_and_setters) first. – marblewraith Jul 29 '15 at 07:41

connexo · Accepted Answer · 2015-07-29T07:57:40.070

The get syntax binds an object property to a function that will be called when that property is looked up.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/get

The more general and exhausting explanation can be found here:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Working_with_Objects#Defining_getters_and_setters

Basically, it allows you to define what happens when a certain object property is read by code. In an analogous fashion, you can also define what should happen when code writes to that property with a set definition. In both cases you overwrite the standard behaviour for that object property.

This is all part of ECMAScript 5.1, and thus, not available in IE < 9.

What does your example code do?

In your example code, you can see that whenever the property DEFAULT_WIDTH is read, a constant value will be returned. I guess the intention of this is to make sure DEFAULT_WIDTH cannot be redefined as some other value (which it in fact can, but reading it will still return 50).

Defining a getter on existing objects using defineProperty

To append a getter to an existing object later at any time, use Object.defineProperty().

var o = { a:0 }
Object.defineProperty(o, "b", { get: function () { return this.a + 1; } });
console.log(o.b) // Runs the getter, which yields a + 1 (which is 1)

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/get#Defining_a_getter_on_existing_objects_using_defineProperty

JavaScript, unknown syntax

2 Answers2

What does your example code do?

Defining a getter on existing objects using defineProperty