- Tags: JS Operator, Math
- Categories: JavaScript Operators, JavaScript Reference, Reference
Quick Reference
JavaScript increment/decrement operators are used to increase or decrease a variable and/or value, and is often used in loops as a way to count iterations.
Increment
The ++ can be placed before or after the variable. This is the same as x = x + 1.
let x = 1;
x++; // x now equals 2
let x = 1;
++x; // x now equals 2
Decrement
The — can be placed before or after the variable. This is the same as x = x – 1.
let x = 10;
x--; // x now equals 9
let x = 10;
--x; // x now equals 9
Post Increment/Decrement vs. Pre Increment/Decrement
Although the ++/– signs can occur before or after the variable, there can be a big difference in the results. When placing the ++ after the variable the value will be returned before the operand is increased.
So in the following z is equal to x BEFORE the incrementation (i.e., z = x THEN x is incremented).
// post incrementation: the ++ is AFTER the variable
let x = 1;
let z = x++; // z = 1, x = 2
And in the following z is equal to x AFTER the incrementation (i.e., z = x AFTER x is incremented).
// pre incrementation: the ++ is BEFORE the variable
let x = 1;
let z = ++x; // z = 2, x = 2
And of course the above similarly applies to post and pre decrement.
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JAVASCRIPT NOTES:
- When using JavaScript, single or double quotation marks are acceptable and work identically to one another; choose whichever you prefer, and stay consistent
- JavaScript is a case-sensitive language; firstName is NOT the same as firstname
- Arrays count starting from zero NOT one; so item 1 is position [0], item 2 is position [1], and item 3 is position [2] … and so on
- JavaScript variables must begin with a letter, $, or _
- JavaScript variables are case sensitive (x is not the same as X)
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