What it exactly means in Javascript (assigning variable)

 

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  • Is there a “null coalescing” operator in JavaScript? 8 answers
  • What does “var FOO = FOO || {}” (assign a variable or an empty object to that variable) mean in Javascript? 7 answers

    • The || is effectively working like a SQL COALESCE statement. 

    var x = y || z;

    means:

    if y evaluates to a "truthy" value, assign y to x .

    if y evaluates to a "falsy" value, assign z to x .

    See http://11heavens.com/falsy-and-truthy-in-javascript for more detail on "truthy/falsy" (or just google it).

    The || is an or operator.

    It basically means if variable is undefined, it will assign variable to a new object literal.

    https://developer.mozilla.org/en-US/docs/JavaScript/Guide/Expressions_and_Operators#Logical_operators

    || does mean OR here: 

    var x = 5
var x = x || {} //If v is defined, v = v, else v = {} (new, empty, object).
//x = 5 since x already was defined

var y = y || {}
//y = {} since y was undefined, the second part is run.
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