Take you to learn the new methods in Es5

1. ES5 Some new methods are added in , Can be very convenient operation array or string , These methods mainly include the following aspects

• Array methods
• String method
• Object methods
  

2. Array methods

Iterative traversal method ：forEach()、map()、filter()、some()、every()
Judgment method ：isArray()

2.1 forEach Follow jQuery Of each Usage is similar. . Grammar is ：

array.forEach(function(currentValue, index, arr))

• currentValue: Array the values of the current item
• index: Array the index of the current item
• arr: Array object itself

var arr = [1,2,3]
arr.forEach(function(value, index, array){
   
	console.log(' Every array element '+ value)
  console.log(' The index value of each array element '+ index)
  console.log(' The array itself '+ array)
})

The operation effect is shown below

2.2 map()

array.map(function(currentValue, index, arr))

map() Method to create a new array , The result is the result returned after each element in the array invokes a supplied function .
Be careful ：map() Method is to return a new array directly

• currentValue: Array the values of the current item
• index: Array the index of the current item
• arr: Array object itself

var array1 = [1, 4, 9, 16];
var map1 = array1.map(function(value, index, arr) {
   
return value * 2
});
console.log(map1) //[2,8,18,32]

2.3 filter()

array.filter(function(currentValue, index, arr))

filter() Method is used to filter to create a new array , The elements in the new array are checked by checking all the eligible elements in the specified array , It is mainly used to filter arrays .
filter() Method is to return a new array directly

• currentValue: Array the values of the current item
• index: Array the index of the current item
• arr: Array object itself

var arr = [12,66,88]
//  Choose greater than 20 Of 
var newarr = arr.filter(function(value, index){
   
  return value >=20
})
 It can be abbreviated as var newarr = arr.filter( //[66, 88])
console.log(newArr) //[66, 88]

The preview effect is shown in the following figure

2.4 some()

array.some(function(currentValue, index, arr))

some() Method is used to detect whether the elements in the array meet the specified conditions , Popular point to find whether there are elements in the array that meet the conditions
Be careful ： some() Method return value is Boolean , If you find this element , Just go back to true, If not found, it will return false
If you find the first element that satisfies the condition , Then stop the cycle , No more searching

• currentValue: Array the values of the current item
• index: Array the index of the current item
• arr: Array object itself

var arr=[10,30,4]
var b = arr.some(function(value){
   
	return value > 20
})
console.log(b) //true

2.5 every()

array.every(function(currentValue, index, arr))

every() Method to test whether all elements in an array can pass the test of a specified function . It returns a Boolean value .
Be careful ：every() Method must be qualified for each element to return true, If one doesn't match , Then return to false.
If you receive an empty array , This method returns in all cases true.

• currentValue: Array the values of the current item
• index: Array the index of the current item
• arr: Array object itself
  

2.6 isArray()

Array.isArray(obj)

Array.isArray() Used to determine if the value passed is a Array

• obj Is the value that needs to be tested . If it is an array, it returns true, Otherwise return to false

difference ：

1. filter It's looking for elements that satisfy the condition , It returns an array , And it's to return all the elements that meet the conditions
2. some It's to find out whether the element that satisfies the condition exists , It returns a Boolean value , If you look for the first element that satisfies the condition , Just stop the cycle . If the array queries for the only element , use some The method is more suitable , Because it finds this element , It's not a cycle , More efficient
3. every It's to find out whether all elements meet the criteria , It returns a Boolean value
4. map Is to create a new array , The result is the result returned after each element in the array invokes a supplied function
   

3. String method

trim() Method to remove white space characters from both ends of a string

str.trim()

trim() Method does not affect the original string itself , It returns a new string .

4. Object methods

Object.defineProperty() Define new properties or modify existing properties in the object

Object.defineProperty(obj, prop, descriptor)

• obj: It's necessary . Target audience
• prop: It's necessary . The name of the property to be defined or modified
• descriptor: It's necessary . Properties owned by the target property

Object.defineProperty() The third parameter descriptor explain ： In the form of objects {} Writing

• value： Set the value of the property , The default is undefined
• writable: Whether the value can be overridden .true | false The default is false
• enumerable: Whether the target property can be enumerated .true | false The default is false
• configurable: Whether the target attribute can be deleted or the attribute can be modified again true | false The default is false

var obj = {
   
id: 1,
pname: ' millet ',
price: 1999
}
// How previous objects add and modify properties 
obj.num = 1000
obj.pirce = 99
console.log(obj)

//Object.deefineProperty() Define new properties or modify existing properties 
Object.defineProperty(obj, 'num',{
   
	value: 1000,
})
Object.defineProperty(obj, 'pricee',{
   
	value: 9.9,
})
Object.defineProperty(obj, 'id',{
   
  // If the value is false, It is not allowed to modify 
	writable: false,
})
Object.defineProperty(obj, 'address',{
   
	value: ' Zhengzhou, China ',
  // If the value is false, Traversal is not allowed , enumeration 
  enumerable: false
})
console.log(obj)
console.log(Object.keys(obj))

summary

This article mainly shares ES5 Some new methods , There are array methods 、 String method 、 Object methods and so on , It mainly shares the usage of GE's method , Characteristics and so on .