What are javascript expressions?

Javascript expressions include: 1. Arithmetic expression; 2. String expression; 3. Main expression; 4. Array and object initializer expression; 5. Logical expression; 6. Left-hand expression Formula; 7. Property access expression; 8. Object creation expression; 9. Function definition expression; 10. Call expression, etc.

The operating environment of this article: Windows 7 system, javascript version 1.8.5, DELL G3 computer

What are the javascript expressions?

An expression is a unit of code that can be evaluated and resolved into a value. Expressions in JS can be divided into several categories.

• Arithmetic expression

• String expression

• Main expression

• Array and object initializer expressions

• Logical expression

• Left side expression

• Property access expression

• Object creation expression

• Function definition expression

• Calling expressions

• Arithmetic expressions

Under this category, take all expressions that evaluate to a number:

1 / 2
i++
i -= 2
i * 2

String expression

Expression that evaluates to a string:

'A ' + 'string'

Main expression

Under this category, variable reference, literal and constants:

2
0.02
'something'
true
false
this //the current object
undefined
i //where i is a variable or a constant

There are also some language keywords:

function
class
function* //the generator function
yield //the generator pauser/resumer
yield* //delegate to another generator or iterator
async function* //async function expression
await //async function pause/resume/wait for completion
/pattern/i //regex
() // grouping

Array and object initializer expressions

[] //array literal
{} //object literal
[1,2,3]
{a: 1, b: 2}
{a: {b: 1}}

Logical expressions

Logical expressions Use logical operators and resolve to Boolean values:

a && b
a || b
!a

Left side expression

new //create an instance of a constructor
super //calls the parent constructor
...obj //expression using the spread operator

Property access expression

object.property //reference a property (or method) of an object
object[property]
object['property']

Object creation expression

new object()
new a(1)
new MyRectangle('name', 2, {a: 4})

Function definition expression

function() {}
function(a, b) { return a * b }
(a, b) => a * b
a => a * 2
() => { return 2 }

Calling expression

Syntax for calling a function or method

a.x(2)
window.resize()

Recommended learning: "js basic tutorial"

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