JavaScript 中
2.2 Basic syntax
1. Variable definition
Variable type variable name = variable value;
2. Conditional control
if else else if
2.3 Data type
Values, text, graphics, audio, video. . . . . .
number
No distinction between decimal and integer
String
‘abc' "abc"
Boolean value
true false
logic operation
&& || !
Comparison operation
== equal to (the type is different, the value is meaningful, and it will be judged as true)
=== Absolutely equal
null和undefined
null empty
undefined
Array
java: a series of identical objects
js: casually defined
var qwe = [1,2,3,4,'qwe',"hello"]
Object
Each attribute is separated by a comma, the last one does not need a comma
2.4 Strict inspection mode
'use strict' to prevent problems caused by randomness
3. Data type
3.1 String
1. We use single quotes and double quotes for normal strings
2. Escape character \
3. Write multi-line strings
var msg = `
hello
world
你好`
4. Template string
let name = "ijuy";
let age = 3;
let msg=`你好，${name}`
5. String
str.length
String variability, immutable
- method
student.toUpperCase () case conversion
student.toLowerCase()
student.substring (1) interception
student.substring(1,3)
3.2 Array
Array can contain any data type
var arr = [1,2,3,4,5,6]
1. Length
arr.length
If the size of the array assigned to arr.length changes
2. indexOf Get subscript index by element
3. slice () intercepts a part of Array and returns a new array, similar to String's substring
4. Push (), pop () stack with open tail
5, unshift (), shift () stack of head opening
6, sort () sort
7, reverse () element reversal
8. Concat () splicing
9, join () uses a specific string connection
10. Multidimensional array
3.3 Object
Several keys
All keys are strings, all values are arbitrary objects
var 对象={
属性名:属性值，
属性名:属性值，
属性名:属性值
}
var person={
name = "ijuy"
}
1. Dynamically delete attributes
delete person.name
true
//原属性name就没了
2. Dynamic addition
person.haha="haha"
3. Determine whether the attribute value is in this object
XXXX in XXXX
'name' in person
3.4 Process control
if judgment
'use strict'
var age = 3;
if(age>3){
alert("haha");
}else{
alert("kuwa!");
}
cycle
'use strict'
var age = 3;
while (age<100){
age=age+1;
console.log(age);
}
for (object in variable) iterative subscript
for (object of variable) iteration content
foreach
3.5 Map Set
Map:
<script>
var map = new Map([['tom',100],['jack',90],['haha',80]])
var name = map.get('tom');
console.log(name);
</script>
Set: Unordered and non-repetitive set
var set = new Set([1,1,1,2,1,2]);
set
Set(2) {1, 2}
3.6 Iterable
Traverse the map
var map = new Map([['tom',100],['jack',90];
for(let x of map){
console.log(x);
}
Traverse set
var set = new Set([1,1,1,2,1,2]);
for(let x of set){
console.log(x);
}