Review of knowledge points:
Function:
Formal and argument, unequal
Short circuit assignment
String splicing (string splicing is used when many values are returned)
Scope!!!!!!
Global, local and scope are relative (the child function can access the variables of the parent function)
Formal parameter: it is essentially a local variable
precompile
Promote var and named functions
// Code is not always executed from top to bottom
console.log(111);
// The event handling function is executed later, that is, only when clicked
document.onclick = function () {
console.log(666);
}
console.log(222);
//Actual sequence
// 111
// 222
// 666
//Click the event to executeFunction: a data type
System function: prompt() confirm() eval()
Recursion: transfer and regression, call yourself
Example of Euclidean finding the greatest common divisor:
// Euclid seeks the greatest common divisor
// 8 12
// 8 / 12 8
// 12 / 8 4
// 8 / 4 0
// 4 / 0
// 3 7
// 3 / 7 3
// 7 / 3 1
// 3 / 1 0
// 1 / 0
// A% B = = = 0 B is the greatest common divisor
function gcd(a , b) {
// if(a % b === 0) {
// return b
// }
// return gcd(b , a % b)
return a % b === 0 ? b : gcd(b , a % b)
}
// When b is 0, a is their greatest common divisor
// function gcd(a,b){
// return b===0?a:gcd(b,a%b);
// }
var res = gcd(28,18)
console.log(res);Arguments accepts argument problems
Arguments can be accepted as a pseudo array, and there are also corresponding arguments Length and subscript can be used when the argument cannot be determined
// In general, formal parameters are used to accept the value of arguments
// You can use arguments to accept arguments
function log() {
// Pseudo array / class array
console.log(arguments);
console.log(arguments[0]);
console.log(arguments[1]);
// console.log(arguments[2]);
console.log(arguments.length);
}
log(1,2)array
(store a set of data of the same data type)
An array is a group of numbers (generally speaking, the data types are the same), which is equivalent to defining many variables of the same data type at one time. If a single variable is a small container, an array is a large container with multiple grids (each grid is a small container).
Array is a data type.
// var a = 1 ;
// var b = 3 ;
// var c = 5 ;
// var d = 2 ;
// Array: stores a set of data of the same data type
var arr = [1,3,5,,2] ;
console.log(arr);
// Array subscript method to access the value of the array: arr[index]
console.log(arr[0]);
// Length of array
console.log(arr.length);
console.log(arr[3]);
// var arr = ['a' , 'b' , 'c'] ;
// var arr = [1,2,'a','b',true] ; // Not very standard
var arr = [1,2,3] ;
console.log(arr[10]); // undefined
// [1,2,3,,,,,,,20]
// In fact, it lengthens the length of the array in disguise
arr[10] = 20 ;
console.log(arr[10]);
console.log(arr.length); // 11
console.log(arr); // var arr = [1,2,3] / / literal declaration
// //An array is an object
// var arr = new Array(1,2,3) ; // Instantiate an object array constructor (used to create objects)
// console.log(arr.length);
// console.log(arr);
// var a = 1 ; // Literal declaration
// var b = new Number(2) ; // Instantiate an object
// console.log(a);
// console.log(b);
// var c = 'hello' ;
// var d = new String('hello') ;
// //When Array has only one parameter, it indicates the length of the Array
// var arr2 = new Array(10) ;
// console.log(arr2);
// Declare an empty array and append values to the array
var arr = [] ;
arr[0] = 'a' ;
arr[1] = 'b' ;
arr[2] = 'c' ;
arr[10] = 'f' ;ergodic
Read each value in the array
Loop and for in are used to traverse the angle of the object
for in will automatically filter null values, which is generally not recommended.
for of traverses the value of the object
// Traversal: read every value in the array
var arr = [1,2,3,4,,,,5] ;
// console.log(arr[0]);
// console.log(arr[1]);
// console.log(arr[2]);
// Loop traversal
// for(var i = 0 ; i < arr.length ; i++) {
// console.log(arr[i]);
// }
// for in is used to traverse the corner mark of the object -- bug (automatically filter out null values)
// for(var i in arr) {
// console.log(arr[i]);
// }
// for of traverses the value of the object
for(var v of arr) {
console.log(v);
}Case: generate a four digit random verification code
function rand(min , max){
return Math.floor(Math.random()*(max - min)+min)
}
var arr = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','1','2','3','4','5','6','A','B','C','D','E','F'];
var res = '';
for(i = 0 ; i < 4 ; i++){
res += arr[rand(0 , arr.length)]
}
console.log(res)Case: find the maximum value in the array
var arr = [10, 3 , 4 , 8 , 56 , 9 , 18];
var max = arr[0];
for(i= 0 ; i < arr.length; i++){
if(max < arr[i]){
max = arr[i]
}
}
console.log(max);Case: bubble sorting
Move a group of numbers one by one, and finally get a group of arrays from small to large
Loop twice. The inner loop is sorted after one-to-one comparison. However, since each number is ranked last, the value of the next number to be compared will be one less. Therefore, the inner loop can be optimized to subtract one cycle i after one less than the length of the loop array.
var arr = [12 , 4 , 6 , 45 , 9 , 8]
for(var i = 0 ; i < arr.length - 1 ; i++){
for(var j = 0 ; j < arr.length - 1 - i; j++){
if(arr[j] > arr[j+1]){
var t = arr[j];
arr[j] = arr[j+1];
arr[j+1] = t
}
}
}
console.log(arr);Cases: selecting sorting
Compare the size of each value in turn. By default, the first value is the minimum. If not, the minimum value will change, and the value of the lower corner will be exchanged with the minimum value. - reduce the number of value exchange by comparing the size in advance
var arr = [12 , 4 , 8 , 9 , 34 , 5];
for(var i = 0 ; i < arr.length - 1 ; i++){
var min = i;
for(var j = i+1 ; j < arr.length ; j++){
if(arr[min] > arr[j]){
min = j
}
}
if(min !== i){
var t = arr[i];
arr[i] = arr[min];
arr[min] = t;
}
}
console.log(arr);Basic method of array
push ， append value to the tail
pop # deletes a value at the end of the array
unshift appends a value to the head of the array
shift deletes a value to the head of the array
// push(v1,v2,v3...) Appends a value to the end of the array
// pop() deletes a value at the end of the array
// unshift() appends a value to the head of the array
// shift() deletes a value to the head of the array
var arr = [1,2,3] ;
// arr[3] = 'a' ;
arr.push('a' , 'b' , 'c') ;
console.log(arr);
arr.pop() ;
console.log(arr);
arr.unshift('hello' , 'hi');
console.log(arr);
arr.shift();
console.log(arr);
var arr2 = [] ;
for(var i = 0 ; i <= 10 ; i++) {
// arr2[i] = i
arr2.push(i)
}
console.log(arr2);push package
/ Append data to an array
// var arr = [1,2,3,4] ;
// arr[arr.length] = 'hello' ;
// console.log(arr);
// function push(n , n2 , n3) {
// var arr = [1,2,3,4] ;
// arr[arr.length] = n ;
// arr[arr.length] = n2 ;
// arr[arr.length] = n3 ;
// console.log(arr);
// }
function push() {
var arr = [1,2,3,4] ;
// Used to accept argument list --- pseudo array
console.log(arguments);
for(var i = 0 ; i < arguments.length ; i++) {
console.log(arguments[i]);
arr[arr.length] = arguments[i]
}
console.log(arr);
}
push('a','b','h' ,'t')pop encapsulation
// Deletes the last value in the array
function pop() {
var arr = [1,2,3,4,5] ;
var arr2 = [] ;
for(var i = 0 ; i < arr.length - 1 ; i++) {
arr2.push(arr[i])
}
console.log(arr2);
}
pop()