What does “options = options || {}” mean in Javascript? [duplicate]

by

This is useful to setting default values to function arguments, e.g.:

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

If you call test without arguments, options will be initialized with an empty object.

The Logical OR || operator will return its second operand if the first one is falsy.

Falsy values are: 0, null, undefined, the empty string (""), NaN, and of course false.

ES6 UPDATE: Now, we have real default parameter values in the language since ES6.

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

If you call the function with no arguments, or if it’s called explicitly with the value undefined, the options argument will take the default value. Unlike the || operator example, other falsy values will not cause the use of the default value.

More Related Contents:

  1. What is “?:” notation in JavaScript?
  2. JavaScript Syntax error
  3. JavaScript property access: dot notation vs. brackets?
  4. What do parentheses surrounding an object/function/class declaration mean? [duplicate]
  5. What does the leading semicolon in JavaScript libraries do?
  6. Why avoid increment (“++”) and decrement (“–“) operators in JavaScript?
  7. Why does ++[[]][+[]]+[+[]] return the string “10”?
  8. What does a tilde do when it precedes an expression?
  9. Why do results vary based on curly brace placement?
  10. How do I convert a float number to a whole number in JavaScript?
  11. Javascript: Get deep value from object by passing path to it as string [duplicate]
  12. Is && statement() the same as if() statement()?
  13. Is localStorage.getItem(‘item’) better than localStorage.item or localStorage[‘item’]?
  14. How can I concatenate regex literals in JavaScript?
  15. Advanced JavaScript: Why is this function wrapped in parentheses? [duplicate]
  16. difference between dot notation and bracket notation in javascript [duplicate]
  17. Dot and Square Bracket Notation
  18. Syntax highlighting code with Javascript [closed]
  19. Difference between var and this in Javascript functions?
  20. “elseif” syntax in JavaScript
  21. What is the decimal separator symbol in JavaScript?
  22. What is the purpose of a semicolon before an IIFE? [duplicate]
  23. How can % signs be used in identifiers
  24. ES6+ javascript module export options
  25. javascript syntax: function calls and using parenthesis
  26. JavaScript dot notation [duplicate]
  27. Using a block’s return value in JavaScript
  28. What’s the reason for using such syntax (0, _.Em)();
  29. JQuery .hasClass for multiple values in an if statement
  30. What does ‘::’ (double colon) do in JavaScript?

Leave a Comment