A Boolean data type represents logical truth and falsehood and has only two values: literals true and false, which are also language reserved words.
Boolean values can be directly assigned to variables or are the result of a comparison.
1 2 3 4 5 | var test1 = false;var test2 = true;var a = 5, b = 5;var test3 = (a == 5); // true |
Boolean values are often used in control structures. In if/else statement for example if a value is true one block of code is executed, if the value is false, then another:
1 2 3 4 5 6 7 | var isFree = false;var price;if (isFree) { price = 0;} else { price = 10;} |
All values in JavaScript can be converted to a boolean value.
Values that are converted to false:
- “” (empty string)
- 0
- NaN
- null
- undefined
Values that are converted to true:
- nonempty strings,
- nonzero numbers,
- objects (and arrays).
Flow control statements automatically perform this conversion:
1 2 3 4 5 6 7 8 9 | var text = "";if (!text) { alert("Text is empty");}var obj = {name: 'Jack'};if (obj) { alert("Object is set");} |
In both cases alerts will be displayed.
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