Here you’ll find everything you need to know about Numbers, Strings, and Operators.
JavaScript has one number type (which is a 64-bit IEEE 754 double).
Doubles have a 52-bit mantissa, which is enough to store integers up to about 9✕10¹⁵ precisely.
3; // = 3
1.5; // = 1.5
Some basic arithmetic works as you’d expect.
1 + 1; // = 2
0.1 + 0.2; // = 0.30000000000000004
8 - 1; // = 7
10 * 2; // = 20
35 5; // = 7
Including uneven division.
5 / 2; // = 2.5
And modulo division.
10 % 2; // = 0
30 % 4; // = 2
18.5 % 7; // = 4.5
Bitwise operations also work; when you perform a bitwise operation your float is converted to a signed int up to 32 bits.
1 << 2; // = 4
Precedence is enforced with parentheses.
(1 + 3) * 2; // = 8
There are three special not-a-real-number values:
Infinity; // result of e.g. 1/0
-Infinity; // result of e.g. -1/0
NaN; // result of e.g. 0/0, stands for 'Not a Number'
There’s also a boolean type:
true;
false;
Strings are created with ‘ or “.'abc';
"Hello, world";
Negation uses the ! symbol
!true; // = false
!false; // = true
Equality is ===
1 === 1; // = true
2 === 1; // = false
Inequality is !==
1 !== 1; // = false
2 !== 1; // = true
More comparisons1 < 10; // = true
1 > 10; // = false2 <= 2; // = true
2 >= 2; // = true
Strings are concatenated with +"Hello " + "world!"; // = "Hello world!"
… which works with more than just strings"1, 2, " + 3; // = "1, 2, 3""Hello " + ["world", "!"]; // = "Hello world,!"
and are compared with < and >"a" < "b"; // = true
Type coercion is performed for comparisons with double equals…"5" == 5; // = true
null == undefined; // = true
…unless you use ==="5" === 5; // = false
null === undefined; // = false
…which can result in some weird behaviour…13 + !0; // 14"13" + !0; // '13true'
You can access characters in a string with charAt"This is a string".charAt(0); // = 'T'
…or use substring to get larger pieces."Hello world".substring(0, 5); // = "Hello"
length is a property, so don’t use ()."Hello".length; // = 5
There’s also null and undefined.
null; // used to indicate a deliberate non-value
undefined; // used to indicate a value is not currently present (although // undefined is actually a value itself)
false, null, undefined, NaN, 0 and “” are falsy; everything else is truthy.
Note that 0 is falsy and “0” is truthy, even though 0 == “0”.