A selection of JavaScript snippets for your quick perusal when you are dashing between billion-dollar ideas.
blah
A plain word refers to a variable in the current environment.
"blah"
A quoted word is a string, a value containing piece of text.
12
A number value.
true
Boolean (yes/no) value. true
for yes, false
for no.
a + b
Binary operator applied to two values. +
to add, -
to subtract, *
to multiply, /
to divide.
(a + b) * c
Parenthesis for explicit grouping.
a < b
: Comparison operators ==
, !=
(not equal), <
, >
, <=
(less or equal), >=
.
a = b
Assignment, set variable a
to value b
. Not to be confused with ==
comparison. a += b
is a shorthand for a = a + b
, also for -=
etc.
a && b
Logical operators — &&
for AND, ||
for OR.
-a
Unary (one-operand) operator. -
to negate (make negative)
!a
Unary (one-operand) operator. !
for boolean negation.
!!a
Using two !
operators to work out if something is Truthey.
a[b]
Subscript, fetch the field named by b
from value a
.
a.x
Shorthand for a["x"]
.
a(b)
Function call. Call the function value a
with b
as argument. Zero or more argument expressions can be given, separated by spaces. a(1, 2, 3, 4)
a.x(b)
Method call. Call the function found in field x
of value a
, and pass a
as the this
argument.
[1, 2, 3, 4]
Array value with zero or more elements.
{a: 1, b: 2}
Object value with zero or more name: value
field definitions.
function(arg1, arg2) {
/* ... body ... */
}
Function value. Zero or more argument names. Any statements may appear in body.
a;
Any expression, followed by a semicolon, is a statement.
var a = b;
Variable definition. The variable with name a
is defined and given value b
. Value is optional. var a;
sets a
to undefined.
function foo(arg1, arg2) {
// code
}
Function definition. Defines variable foo
to have a function value. Zero or more arguments, any statements may appear in body.
if (a) {
// code if expression true
} else {
// code if expression false
}
Conditional statement. If value a
is true, the first statement, otherwise the else statement executes. Else part may be left off.
if (a) {
// code
} else if (b) {
// code
} else {
// code
}
Chaining conditional expressions.
while (a) {
// code to execute in the loop
}
A while loop. The loop body statement will be executed as long as a
produces a true value.
for (var a = 0; a < 10; a++) {
// code
}
Example for
-loop statement. var a = 1
initializes the loop, a < 10
checks whether it has ended yet, and a++
moves to the next step by incrementing the counter a.
return a;
Only valid inside a function or after a control flow struction like if
. Returns value a
as the result of the function call.
document
An object-orientated representation of the HTML that was read by the browser.
var greeting = document.getElementById("hello")
Search for an element with the id of hello
in the document and assign to the variable greeting
(can be named anything.
var divs = document.getElementsByTagName("div")
Search for all div tags within the document using the html tag.