join 数组转 字符串 ，指定间隔符
var list =[ ‘a’ , ‘b’ , ‘c’ , ‘d’ ]
var str = list . join ( “,” )
console . log ( str ) //a,b,c,d
pop 数组删除删除最后一个元素,返回删除的元素
var list =[ ‘a’ , ‘b’ , ‘c’ , ‘d’ ]
var p = list . pop ()
console . log ( p ) //d
console . log ( list ) //[‘a’,’b’,’c’]
shift 从数组中删除第一个元素,返回删除的元素
var s = list . shift ()
console . log ( s ) //a
console . log ( list ) //[‘b’,’c’]
push 数组结尾添加元素并返回新数组的长度
var list =[ ‘a’ , ‘b’ , ‘c’ ]
var i = list . push ( ‘d’ );
console . log ( i ); //4
console . log ( list ) //[‘a’,’b’,’c’,’d’]
unshift 数组开头添加元素并返回新数组的长度
var j = list . unshift ( ‘x’ )
console . log ( j ); //5
console . log ( list ) //[‘x’,’a’,’b’,’c’,’d’]
splice(x,y) 第一个参数添加新元素的位置、第二个参数删除多少个元素
var list =[ ‘a’ , ‘b’ , ‘c’ ]
//splice 向数组添加新元素
var a = list . splice ( 2 , 0 , “m” , “n” );
console . log ( list ) //[‘a’,’b’,’m’,’n’,’c’]
//splice 删除元素
var list =[ ‘a’ , ‘b’ , ‘c’ ]
var a = list . splice ( 0 , 1 )
console . log ( a ); //[‘a’]
console . log ( list ) //[‘b’,’c’]
concat 合并数组
var list1 = [ ‘a’ , ‘b’ ]
var list2 = [ ‘m’ , ‘n’ ]
var newList = list1 . concat ( list2 )
console . log ( list1 ) //[‘a’,’b’]
console . log ( newList ) //[‘a’,’b’,’m’,’n’]
slice 裁剪数组,返回新数组，它不会从原数组中删除任何元素
var list = [ ‘a’ , ‘b’ , ‘c’ ]
var newList = list . slice ( 1 )
console . log ( newList ) //[‘b’,’c’]
console . log ( list ) //[‘a’,’b’,’c’]
var newList = list . slice ( 1 , 2 )
console . log ( newList ) //[‘b’]
console . log ( list ) //[‘a’,’b’,’c’]
sort 排序，改变原数组
var points = [ 40 , 100 , 5 , 25 ];
points . sort ( function ( a , b ){ return a – b });
console . log ( points ) //[5,25,40,100]
reverse 反转数组
points . reverse ()
console . log ( points ) //[100,40,25,5]
forEach 数组遍历
var list =[ 1 , 2 , 3 , 4 , 5 ]
list . forEach ( item => {
console . log ( item )
})
filter 数组过滤 ,不改变原数组，返回新数组
var nums = [ 45 , 4 , 9 , 16 , 25 ];
var over10 = nums . filter ( item => item > 10 )
console . log ( nums ) //[45, 4, 9, 16, 25]
console . log ( over10 ) //[45, 16, 25]
some 检查某些数组值是否满足条件 返回true,false
var nums = [ 45 , 4 , 9 , 16 , 25 ];
var over10 = nums . some ( item => item > 10 )
console . log ( over10 ) //true
indexOf 在数组中搜索元素值并返回其位置,没有返回-1
var nums = [ 45 , 4 , 9 , 16 , 25 ]
var idx = nums . indexOf ( 9 )
console . log ( idx ) //2
var idx = nums . indexOf ( 10 )
console . log ( idx ) //-1
find 返回满足条件的第一个数组元素的值,没有返回undefined
var nums = [ 45 , 4 , 9 , 56 , 25 ]
var mum = nums . find ( item => item > 50 )
console . log ( mum ) //56
findIndex 返回满足条件的第一个数组元素的索引，没有返回-1
var nums = [ 45 , 4 , 9 , 56 , 25 ]
var mum = nums . findIndex ( item => item > 10 )
console . log ( mum ) //0
