What Does the = _ Operator Do in JavaScript?

Understanding the = _ Operator in JavaScript

In JavaScript, the = _ operator is used for assignment, but with a twist that affects the value of the variable being assigned.

Operator Meaning

The = _ operator consists of three parts:

• =: Assignment operator
• : Unary plus operator
• _: Variable placeholder

Operand Conversion

The unary plus operator ( ) attempts to convert its operand to a number. This means that if the operand is not already a number, the operator will try to cast it into one. This includes strings representing integers or floats, as well as the values true, false, and null. If the conversion fails, the result will be NaN.

Simplified Syntax

The equivalent simplified syntax for the expression r = _:

r = Number(_);

Example

Consider the following code:

<code class="javascript">hexbin.radius = function(_) {
   if (!arguments.length)
       return r;
   r = +_;
   dx = r * 2 * Math.sin(Math.PI / 3);
   dy = r * 1.5;
   return hexbin;
};</code>

In this example, the function hexbin.radius takes a parameter _, which is assigned to the variable r. The operator ensures that r is converted to a number before it is used in subsequent operations. This ensures consistency in type and precision during the calculation of dx and dy.

Performance

According to the MDN documentation, the unary plus operator is the fastest and preferred method for converting non-numbers to numbers in JavaScript. This makes it a valuable tool for optimizing code performance.

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