Array common methods
push()To the arrayThe backInserts one or more elements and returns the resultThe length of the array. (Changes the original array)pop()Delete from arrayThe last element, returns the result isThe deleted element. (Changes the original array)unshift()In the arrayThe front ofInserts one or more elements and returns the resultThe new length of the array. (Changes the original array)shift()Delete from arrayThe first element, returns the result isThe deleted element. (Changes the original array)
var arr = ["a"."b"."c"."d"."e"]
var arrPush = arr.push("ok")
console.log(arrPush); / / 6
var arrPop = arr.pop("ok");
console.log(arrPop);//ok
var arrUnshift = arr.unshift("skr"."ok")
console.log(arrUnshift);/ / 7
var arrShift = arr.shift();
console.log(arrShift); //skr
Copy the codeslice()From an array ofextractOne or more of the specified elements is returned asNew array. (Does not change the original array)
New array = original array. Slice (start index position, end index position); Before closed after openingCopy the code var arr = ["a"."b"."c"."d"."e"]
var result1 = arr.slice(2);// Start with the second value
var result2 = arr.slice(-2);// Extract the last two elements
var result3 = arr.slice(1.3);// Extract the index from the first to the fourth value (but not the fourth)
var result4 = arr.slice(4.0);/ / empty
console.log(result1);// ["c", "d", "e"]
console.log(result2);//["d", "e"]
console.log(result3);//["b", "c"]
console.log(result4);/ / []
Copy the codeSlice () converts a pseudo-array to a true array:
array = Array.prototye.slice. Call (arrayLike) or array = []. Call (arrayLike) or array =Array.from(arrayLike)// New API in ES6
Copy the codesplice()From an array ofdeleteOne or more of the specified elements is returned asNew array. (Changes the original array)
New array = old array.splice (start index index, number to delete, content added); Elements can be deleted or addedCopy the code var arr = ["a"."b"."c"."d"."e"]
var result1 = arr.splice(1.0."boy");// Delete 0 content, add element from index 1
var result2 = arr.splice(1.1);// Delete an element, return the value of the deleted element
var result3 = arr.splice(1.2."skr");// Remove two elements and add a new one
console.log(arr);//["a", "boy", "b", "c", "d", "e"]
console.log(result1);/ / []
console.log(result2);//["boy"]
console.log(result3);//["b", "c"]
console.log(arr);//["a", "skr", "d", "e"]
Copy the codeconcat()Joins two or more arrays and returnsNew array. (Does not change the original array)
New array = old array. Concat (Array one, array two...)Copy the code var arr1 = [1.2.3];
var arr2 = ["a"."b"."c"];
var arr3 = ["one"."two"."three"];
var newArr1 = arr1.concat(arr2);
var newArr2 = arr1.concat(arr2, arr3);
console.log(newArr1); //[1, 2, 3, "a", "b", "c"]
console.log(newArr2); // [1, 2, 3, "a", "b", "c", "one", "two", "three"]
Copy the codejoin()Converts an array to a string, returning the resultConverted string. (Does not change the original array)
New string = original array. Join (parameter);// Optional
Copy the code var arr = ["A"."B"."C"."D"];
console.log(arr.toString()); //A,B,C,D
var str1 = arr.join(); // Same as toSting() when no arguments are passed
var str2 = arr.join("-"); // The argument passed in can be used as a string split symbol
var str3 = arr.join(""); // Passing null does not require a split symbol
console.log(str1); //A,B,C,D
console.log(str2); //A-B-C-D
console.log(str3); //ABCD
Copy the code9. Reverse () reverses the array, and returns an array that is reversed. (Changes the original array)
Reverse array = array.reverse ();Copy the code var arr = ["A"."B"."C"."D"];
var arrReverse = arr.reverse();
console.log(arrReverse);//["D", "C", "B", "A"]
Copy the code10. Sort () sorts the elements of an array from smallest to largest in Unicode by default. (Changes the original array)
When sort() is used without arguments, it defaults to sorting from smallest to largest in Unicode encodingCopy the code var arr1 = ["2"."50"."100"."8"."44"]; // When the array is a string
var newArr = arr1.sort(); // Compare to the Unicode encoding of the first value of the string
console.log(newArr); //["100", "2", "44", "50", "8"]
var arr2 = [2.56.400.12.30.6]; // When the array is a string
var newArr = arr2.sort(); // The first value of the string is compared to the Unicode encoding
console.log(newArr); //[12, 2, 30, 400, 56, 6]
Copy the codeIf we take arguments in the sort() method, we can customize the sorting by adding a callback function that defines two arguments that the browser will call using elements from the array as arguments. Sort by return value:
- If a value greater than 0 is returned, the elements alternate positions
- If a value less than 0 is returned, the element position remains the same
- If 0 is returned, the two elements are equal and the positions are not swapped
var arr3 = [45.88.11.66.100];
var newArr1 = arr3.sort(); //[100, 11, 45, 66, 88]
console.log(newArr1);
var fn = function (a, b) {
if (a > b) {
return 1;
} else {
return -1; }};var newArr2 = arr3.sort(fn);
console.log(newArr2); //[11, 45, 66, 88, 100]
Copy the codeArray traversal
forEach()No return value, similar to the for loop
var hotModel = yidianzu.data.hotModel;
console.log(hotModel);
for (var i = 0; i < hotModel.length; i++) {
console.log(i);
console.log(hotModel[i]);
}
var fn = function (item, index, arr) {
//item:hotModel[i] index:i arr:hotModel
console.log(item);
console.log(index);
};
hotModel.forEach(fn);
Copy the codeFunction principle:
var fn = function (item, index, arr) {
//item:hotModel[i] index:i arr:hotModel
console.log(item);
console.log(index);
};
hotModel.forEach(fn);
//forEach function principle
hotModel.__proto__.forEvery = function (fn) {
for (var i = 0; i < this.length; i++) {
// This refers to hotModel
fn(this[i], i, this); }}; hotModel.forEvery(fn);Copy the code2. Map () processes each item of the array to form a new array (without changing the original array)
var arr = [1.2.3.4.5];
var fn = function (item, index) {
return item + 10;
};
var arr2 = arr.map(fn);
console.log(arr2); //[10,11,12,13,14,15] returns a new array, which is the modified array of map
Copy the codeThe function principle
var arr = [1.2.3.4.5];
var fn = function (item, index) {
return item + 10;
};
var arr2 = arr.map(fn);
console.log(arr2); //[10,11,12,13,14,15] returns a new array, which is the modified array of map
// Map function principle
arr.__proto__.forMap = function (fn) {
var newArr = [];
for (var i = 0; i < this.length; i++) {
/ / I: index values
//this[i] = arr[i]
//this:arr
newArr.push(fn(this[i], i, arr));
}
return newArr; // Map has return values
};
var arr3 = arr.forMap(fn);
console.log(arr3); / /,11,12,13,14,15 [10]
Copy the code3. Filter () runs the callback function on each item in the array, and returns true to form a new array. (Does not change the original array).
var arr = [1.2.3.4.5.6];
var arr2 = arr.filter(function (item, index) {
if (item > 3) {
return true;
} else {
return false; }});console.log(arr2); / / (4 and 6)
Copy the codeFunction principle:
var arr = [1.2.3.4.5];
var fn = function (item, index, arr) {
if (item > 2) {
return true;
} else {
return false; }};var arr2 = arr.filter(fn);
// Returns a new array, the filtered array
console.log(arr2); / / / three, four, five
// Map function principle
arr.__proto__.forMap = function (callBack) {
var newArr = [];
for (var i = 0; i < this.length; i++) {
// This refers to the current array arr--> arr.formap (fn)
/ / I: index values
//this[i] = arr[i]
//this:arr
var isSava = callBack(this[i], i, this);
/ / isSave to a Boolean value
if (isSava) {
newArr.push(this[i]); }}return newArr;
};
var arr3 = arr.forMap(fn);
console.log(arr3); / / / three, four, five
Copy the code4. Stop every() if one of the items returns false, this method returns false.
//every is used to determine whether all arrays meet the criteria
var arr = [80.50.100.200.300];
var isArr =arr.every(function(item,index,arr){
if(item>100) {return true;
}else{
return false}})if(isArr){
console.log("All numbers are greater than 100.")}else{
console.log("There are numbers less than 100.") // There are numbers less than 100
}
Copy the codesome()If one of the entries returns true, the traversal is stopped, and this method returns true.
var arr = [80.50.100.200.300];
var isArr =arr.some(function(item,index,arr){
if(item>100) {return true;
}else{
return false}})if(isArr){
console.log("At least one number is greater than 100.")// At least one number is greater than 100
}else{
console.log("There are numbers less than 100.")}Copy the codereduce()Performs a callback function for each element in the array.
Reduce () requires traversal of the content and can be used to output a result
var arr = [80.50.100.200.300];
var sum =arr.reduce(function(value,item,index,arr){
//value is the initial value. The current initial value is 0
return value+item;
},0)
console.log(sum);/ / 730
Copy the codeOther methods of arrays
Indexof () and lastIndexof ()
Indexof (value) : index from front to back to get the index value of the first occurrence of the element = array. LastIndexof (value) : Index back to the last occurrence of the index value of the element = array. These two methods can be used to determine whether there is a value in the element, if not, return -1.
var arr = ["Cold"."Cruel"."Back to life"."Iron hand"];
var result1 = arr.indexOf("Cruel");
var result2 = arr.lastIndexOf("Iron hand");
var result3 = arr.indexOf("Kris Wu");
console.log(result1);/ / 1
console.log(result2);/ / 3
if(result3 == -1) {console.log("The data doesn't exist.")// Data does not exist
}else{
console.log("Data exists")}Copy the code2. Find () finds the first element that meets [returns true for the specified condition]. Once the first element is found, no further traversal is performed.
find(function(item,index,arr){
return true
})
Copy the code var arr = [12.52.62.32.12];
var result = arr.find(function(item,index){
return item>30
})
console.log(result);/ / 52
Copy the codefindIndex()Find the index value that meets the condition
var arr = [12.52.62.32.12];
var result = arr.findIndex(function(item,index){
return item>30
})
console.log(result);/ / 1
Copy the codeArray.from()Traverses the pseudo-array through the real array
Array.prototype is not in the pseudo-array prototype chain, while array. prototype is in the real Array. So there are no array-related methods in pseudo-arrays.
var fn = function(){
console.log(arguments)
var arr= Array.from(arguments);
console.log(arr);/ / [1, 2, 3]
}
fn(1.2.3);
Copy the codeArray.of()Converts a series of values to an array
var arr = Array.of(value1,value2,.....)
var Ary = Array.of(1."one"["Two"."three"])
console.log(Ary)//[1, "one", Array(2)]
Copy the code