Js object key: plus value syntax

2018-06-26 10:19:53

This question already has an answer here:

What does = +_ mean in JavaScript 12 answers

This is a unary conversion. It's a shorthand method to convert to a number. From the ECMAScript docs:

The unary + operator converts its operand to Number type.

The production UnaryExpression : + UnaryExpression is evaluated as follows:

Let expr be the result of evaluating UnaryExpression.

Return ToNumber(GetValue(expr)).

var a = "45"; //typeof String
a = +a; // now typeof Number

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