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What does the "({})" do in Javascript?

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Just like the one displayed in the image. I am trying to know what does "({})" stand for and what’s the specific meaning for it.

Page({     // Here

})

Looked for it up in search engines, no useful results showed up.

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4

Answers


  1. 0

    {} in JavaScript is an object literal:

    let obj = {
    // properties go here
    // can be empty
};
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  2. 0

    Page() is a call of a function named Page with possible arguments between parenthesis.

    {} is an empty object literal.

    So the Page({}) is a call with 1 argument being an empty object passed to a function being called.

    But we have another context where we could encounter ({}).

    {} could be also a block of statements inside the parenthesis, for example { const test = true }. A block his own scope where we can declare variables belonging to the block only. We use blocks as function bodies also. In an arrow function we have an interesting case:

    () => {} – basically that’s an arrow function with an empty block/body. But an arrow function could be bare (without a block) so in that case it returns the result of the expression after =>. Since {} is reserved for a function body, to return an object as an expression we should use:

    () => ({}).

    Another interesting case when should use () with {} to avoid {} being interpreted as a block is object assignment destructuring:

    let prop1, prop2;
({prop1, prop2} = {prop1: 1, prop2:2});
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  3. 0

    In order to understand what ({}) means, you need to understand what {} and () might mean.

    {}:

    • object literal: {a: 1, b: 2}, in which case an object is defined/created
    • function block: function() {} or () => {} which specifies a function, but this is not your case, because this would have something else besides the {}
    • etc. (code block, substring, like "({})")

    ():

    • function parameter list, like foo(param1, param2)
    • paranthesis operator, like (a + b) * c

    Now, your example is clearly a function call and an object literal being passed to that function. Example:

    function foo(obj) {
    console.log(obj);
}

foo({a: 1, b: 2, c: 3})

    Here we can see that we have a function that takes a parameter and console-logs it out. We call this function, i.e., execute it and pass an object to it, so the object is logged to the console via the function.

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  4. 0

    () has two meanings in Javascrip, one is function call, and the other is grouping. From this point of view, it should mean grouping, like this (1+2)x3.If it is a function, then the Function keyword needs to be used together.

    {} can be represented as an object literal or a local scope. If it is a local scope, then some keywords need to be followed, such as for, function, etc. So this should be expressed as an object literal.

    Combined, it should be a very high priority to create an anonymous object literal.

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