17 commonly used array methods and example demonstrations of vue

let arr = [1,2,3,4,5];
let str = (',');
(str) // -> '1,2,3,4,5';

let arr = ['Zhang San','Li Si','Wang Wu'];
let count = ('Maliu');
(arr) // -> ['Zhang San','Li Si','Wang Wu','Ma Liu'](count) // -> 4
 
let item = ();
(item) // -> Maliu;

let arr = ['Zhang San','Li Si','Wang Wu'];
let item = ();
(arr) // -> ['Li Si','Wang Wu'](item); // -> Zhang San 
let count = ('Maliu');
 
(arr) // -> ['Ma Liu','Li Si','Wang Wu'](count) // -> 3

let arr = [1,2,3,4,5];
let arr1 = ();
(arr1) // -> [5,4,3,2,1]
(arr) // -> [5,4,3,2,1]

let arr = [12,2,43,5,2,5];
(()) // -> [12, 2, 2, 43, 5, 5]
// Note: Through the above case, you will find that the comparison between the printed array and the original array still changes [12,2,43,5,2,5] -> [12, 2, 2, 43, 5, 5]; but has the result we want achieved, why is this?// Because sorting is for character sorting, first use the toString() method of the array to convert it to a string, and then compare bit by bit. 3 is greater than 12, because the first bit is 3>1, so don't be confused with the Number type data sorting.5.1What if you need numerical sorting？
 
// If numerical sorting is required, sort(callback) needs to pass in a callback culvert. The function should have two parameters, compare these two parameters, and then return a number (a-b) that illustrates the relative order of these two values;For example：
let arr = [12,2,43,5,2,5];
(((a,b)=>a-b)) // -> [2, 2, 5, 5, 12, 43]

// Note: slice (startIndex, endIndex) can have two parameters. startIndex is required, indicating which bit starts from; endIndex is optional, indicating which bit end (excluding the endIndex bit), omitting to the last bit; startIndex and endIndex can both be negative numbers. When negative numbers are counted from the last bit, such as -1 means the last bit.let arr =  ['Zhang San','Li Si','Wang Wu','Maliu'];
((1,3)); // -> ['Li Si', 'Wang Wu'](arr) // -> ['Zhang San','Li Si','Wang Wu','Ma Liu']; The original array has not changed.

// Note: splice(start,num,val1,val2,...); All parameters are optional.  Compared with slice, splice will change the original array.// start is the starting position, which can be a negative number. -1 means starting from the last bit, num means the length to be deleted or replaced, and cannot be a negative number.let arr = ['Zhang San','Li Si','Wang Wu','Maliu'];
((2,1)) // -> ['Wang Wu'](arr) // -> ['Zhang San','Li Si','Ma Liu'] 
let arr = ['Zhang San','Li Si','Wang Wu','Maliu'];
((2,1,'Qiro')) // -> ['Wang Wu'](arr) // -> ['Zhang San', 'Li Si', 'Qilang', 'Ma Liu']

let arr = [1,2,3,4,5,6];
(()) // -> '1,2,3,4,5,6'
// Note: No parameters.

// Note: indexOf(value, start); value is the data to be queryed; start is optional, indicating the location where the query starts. When start is a negative number, it goes forward from the tail of the array; if the query cannot exist, the method returns -1 
let arr = ['Zhang San','Li Si','Wang Wu','Maliu'];
(('Li Si')) // -> 1
(('Li Si',2)) // -> -1
()
ES5New methods，Used to traverse arrays，No return value，

// Note: forEach(callback); callback has three parameters by default, namely value (data of the array traversed), index (corresponding index), and self (array itself).let arr = ['Zhang San','Li Si','Wang Wu','Maliu']
let a = ((item,index,self)=>{
    (value + "--" + index + "--" + (arr === self));
})
// The print result is:// Zhang San--0--true// Li Si--1--true// Wang Wu--2--true// Maliu--3-true(a);  // -> undefined---forEach does not return a value//This method is a traversal method and will not modify the original array

//Note: map(callback); callback has three parameters by default, namely value, index, and self.  The same as the forEach() parameter abovelet arr = ['Zhang San','Li Si','Wang Wu','Maliu'];
let arr1 = (item => {
    return 'Hello:'+item
})
(arr1) // -> ['Hello: Zhang San', 'Hello: Li Si', 'Hello: Wang Wu', 'Hello: Ma Liu']

// Note: filter(callback); callback has three parameters by default, namely value, index, and self.let arr = [1,2,3,4,5,6];
let arr1 = ((value,index,self)=>{
    (item) // -> 1,2,3,4,5,6
    (index) // -> 0,1,2,3,4,5
    (self) // -> [1,2,3,4,5,6]
    return item > 3
})
 
(arr1) // -> [4,5,6]

let arr = ['Zhang San','Li Si','Wang Wu','Maliu'];
let str = (item => item == 'Li Si');
(str); // -> 'Li Si'

let arr = ['Zhang San','Li Si','Wang Wu','Maliu'];
let index = (item => item == 'Li Si');
(index); // -> 1;

// Note: every() receives a callback function as a parameter. This callback function needs to have a return value. Every(callback); callback has three parameters by default, namely value, index, and self.let arr = [1,2,3,4,5,6];
let bool = (item => item > 0);
(bool); // -> true;
 
let bool = (item => item > 3);
(bool); // -> false;

//Note: some() receives a callback function as a parameter. This callback function needs to have a return value. Some(callback); callback has three parameters by default, namely value, index, and self.let arr = [1,2,3,4,5,6];
let bool = (item => item > 3);
(bool) // -> true;
 
let bool = (item => item > 6);
(bool) // -> false;

// Note: Parameters: reduce() receives one or two parameters: the first is a callback function, which represents the function called on each item in the array; the second parameter (optional) is used as the initial value of the merge, and is received by the first parameter when the callback function is executed for the first time.  reduce(callback, initial); callback has four parameters by default, namely prev, now, index, and self.  Any value returned by callback will be used as the first parameter for the next execution.  If the initial parameter is omitted, the first iteration occurs on the second term of the array, so the first parameter of the callback is the first term of the array, and the second parameter is the second term of the array. 
let arr = [10,20,30,40,50];
let sum = ((prev,now) => prev+now)
 
(sum); // -> 150;
 
let sum = ((prev,now) => prev+now,110)
 
(sum)