An array of topics
Operators Expand
... use the symbol, the array can be "expanded."
Expanded array of magical ...
eg:
// instead of apply
const foo = [1, 2, 3]
const bar = [4, 5, 6]
foo.push (bar ...) // corresponds foo.push (4, 5, 6)
// false array to a true array
var nodeList = document.querySelectorAll('div')
var earlArray = [...nodeList]
// concat complex operations like in place of, the array structure
var parts = ['shoulders', 'knees'];
var lyrics = ['head', ...parts, 'and', 'toes'];
find and findIndex
Recommendation: Do not use a for loop or forEach or filter to find an element of the array!
Highlights:
The difference findIndex and indexOf
indexOf only incoming value
eg: find within the index element of the array is equal to 2
const arr = [1,2,3,4,5];
const ret = arr.indexOf(2);
findIndex can pass expressions
eg: Find the index value is greater than a first element 2
const arr = [1,2,3,4,5];
const ret = arr.findIndex(el=>{el>2});
expand:
a map is used to map the array of another array
eg: all of the values in the array is multiplied by 2
const arr = [1,2,3,4,5];
const arr2 = arr.map(el=>{return el * 2})
to reduce by a certain operation merge array elements
eg: all the elements in the array is multiplied by
const arr = [1,2,3,4,5];
const ret = arr.reduce((prev, el)=>{return el * prev}, 1)
filter used to filter array elements satisfying the conditions
eg: greater than 2 within the array element screened
const arr = [1,2,3,4,5];
const arr2 = arr.filter(el=>{return el > 2})
some used to determine the array element satisfies certain conditions have not (yet at least satisfies returns true not satisfy a return false)
eg: determining whether there is the element of the array is greater than a 2
const arr = [1,2,3,4,5];
const ret = arr.some(el=>{return el > 2})
for every element in the array is determined not satisfy certain conditions (all not met must meet satisfy returns true return false)
eg: the determination of all array elements is greater than 2
const arr = [1,2,3,4,5];
const ret = arr.every(el=>{return el > 2})
forEach used for traversal (unless you are using forEach to write shorter code, do not use)
find and findIndex used to find qualified elements
eg: Find the index value is greater than the element 5
const arr = [2,4,6,8,10];
const value = arr.find (el => {return el> 5}); // Find the first value is greater than five
const index = arr.findIndex (el => {return el> 5}); // Find the first index is larger than five
includes
includes an array is not used to determine a value comprising
Points
And includes the difference between the indexOf
includes 返回 true or false
indexOf Returns the index can not find the find is returned or -1
eg: 2 determines whether or not included
const arr = [1,2,3,4,5];
const ret1 = !arr.includes(2);
const ret2 = (arr.indexOf(2) === -1);
Function topics
Operators Expand
Parameter expansion
function fn(...params){
}