What does \"options = options || {}\" do in JavaScript?

Understanding "options = options || {}" in JavaScript

When encountering a code snippet like "options = options || {};", it raises questions about its functionality. This snippet is often used to set default values for function arguments.

The core of this expression lies in the logical OR (||) operator. This operator evaluates its operands in order, returning the first truthy value it encounters or the last value if all are falsy. In this case, "options" is evaluated first. If "options" is falsy (undefined, null, 0, "", etc.), it evaluates to false and the expression becomes "options || {}".

The "{}" is a JavaScript object literal, representing an empty object. Therefore, if "options" is initially undefined, this expression assigns an empty object to the "options" variable. If "options" already exists, the evaluation stops as "options" is a truthy value.

This pattern is used to initialize function arguments with default values when they are passed as undefined. For instance:

function test(options) {
  options = options || {};
}

When this function is called without arguments, "options" is assigned an empty object. If "options" is explicitly passed as undefined, it also takes the default value.

ES6 Update

ES6 introduced default parameter values, making this expression obsolete for setting defaults. In ES6, you can set default values using the following syntax:

function test(options = {}) {
  //...
}

With this syntax, if "options" is passed as undefined or is explicitly set to undefined, it takes the default value of an empty object. Unlike the || operator pattern, other falsy values will not trigger the use of the default value.

The above is the detailed content of What does \"options = options || {}\" do in JavaScript?. For more information, please follow other related articles on the PHP Chinese website!