What does = +_ mean in JavaScript

by 
r = +_;
  • + tries to cast whatever _ is to a number.
  • _ is only a variable name (not an operator), it could be a, foo etc.

Example:

+"1"

cast “1” to pure number 1.

var _ = "1";
var r = +_;

r is now 1, not "1".

Moreover, according to the MDN page on Arithmetic Operators:

The unary plus operator precedes its operand and evaluates to its
operand but attempts to converts it into a number, if it isn’t
already. […] It can convert string representations of integers and
floats, as well as the non-string values true, false, and null.
Integers in both decimal and hexadecimal ("0x"-prefixed) formats are
supported. Negative numbers are supported (though not for hex). If it
cannot parse a particular value, it will evaluate to NaN.

It is also noted that

unary plus is the fastest and preferred way of converting something into a number

More Related Contents:

  1. Is there a “null coalescing” operator in JavaScript?
  2. Question mark and colon in JavaScript
  3. What is the difference between the `=` and `==` operators and what is `===`? (Single, double, and triple equals)
  4. What is the JavaScript >>> operator and how do you use it?
  5. Why does JavaScript handle the plus and minus operators between strings and numbers differently?
  6. What do these JavaScript bitwise operators do?
  7. Are Variable Operators Possible?
  8. Why does (0 < 5 < 3) return true?
  9. Javascript: operator overloading
  10. What does the ^ (caret) symbol do in JavaScript?
  11. What is the instanceof operator in JavaScript?
  12. How does !!~ (not not tilde/bang bang tilde) alter the result of a ‘contains/included’ Array method call?
  13. What is the !! (not not) operator in JavaScript?
  14. JavaScript comparison operators: Identity vs. Equality
  15. Why does a shift by 0 truncate the decimal?
  16. What does the || operator do?
  17. What is the difference between != and !== operators in JavaScript?
  18. Understanding Incrementing
  19. Can I use chained comparison operator syntax? [duplicate]
  20. What do “>>” and “
  21. How does !!~ (not not tilde/bang bang tilde) alter the result of a ‘contains/included’ Array method call?
  22. && operator in Javascript
  23. What is “?:” notation in JavaScript?
  24. What is the difference between the = and == operators, and what is ===?
  25. spread operator vs array.concat()
  26. How can I round to whole numbers in JavaScript?
  27. Is it possible to create custom operators in JavaScript?
  28. What’s the difference between ( | ) and ( || )?
  29. Logical operator && and two strings in javascript
  30. What does “!” operator mean in javascript when it is used with a non-boolean variable?

Leave a Comment