A js
1. The width and height of the visible region
① width document.documentElement.clientWidth // visible area
document.documentElement.clientHeight // highly visible area
② width 100 vw // visible area
Highly visible area of 100 vh //
vw: 1vw equal to 1% of the width of the viewport
vh: 1vh equal to 1% of the height of the viewport
2. Regular Expressions
Regular expression describes a set of strings, a string can be used to check if they contain a certain substring matching string will replace or remove the string meet a certain criteria from a string. ,
Access: 1. As long as the rule-fuzzy match multiple keyword 2. As long as according to the rules for compliance verification string
Use: 1. directly only by positive amount: var reg = / regular / ig; 2. with new: var reg = new RegExp ( "regular", "ig");
String commonly used in regular API:
Search:
1. Find keywords appear in a fixed position
var i = str.indexOf ( "keyword", fromi)
var i = str.lastIndexOf ( "keyword", fromi)
2. determine whether that comply with the rules Keywords:
var i = str.search (/ 正 则 / in)
3. Obtain all the keywords contents:
var i = str.match (/ regular / ig); if not g: match the equivalent of search, except that Image content can be obtained: [0: "keyword", index: i]
4. That content is obtained for each keyword, and obtaining the position of each keyword: reg.exec (str)
replace:
Abbreviations: All words will be replaced with a uniform replacement value
str = str, replace (/ regular / ig, 'substitute value')
Advanced: According to different keywords, substitute different values
str = str.replace (/ regular / ig,
function(kw,$1,$2,...){
return value is determined according to different alternatives return kw
)
Delete: Replace the keyword ''
Cutting: var subStrs = str.split (/ regular /);
3.isNaN()
isNaN () function is used to check whether the non-numeric parameter.
isNaN(233); false
isNaN (Ni); true
4. rounding to two decimal places or
rounding:
1. and num = 2.3362412322;
num = num.toFixed (2); // output 2.34
No rounding:
2.Math.floor (15.66842340 * 100) / 100 // output 15.66
3.Number (. 15.66842340.toString () match (/ ^ \ d + (:?.? \ \ D {0,2}) /)) // output 15.66
4. Share the classic solution:
ToSei
parseInt(2.56789) //2
Math.ceil(2.567) //2
Math.ceil(2.56789) //3
Math.round(2.5678) //3
m^0
m|0
m>>>0
connection:
var newArr = arr1.concat (arr2); // after the spliced arr2 arr1, returns a new array
Note: concat authority to modify the original array, only to return a new array, you must catch the result of splicing with variables.
concat may be any type of parameter can be an array, number, string
If .concat (value 1, value 2, arr2, ....) ;, then .concat array type parameters may be broken down to a single value.
Interception sub-array:
var subArr = arr.slice (starti, endi + 1); // arr taken in starti subarray position to the end position endi.
Note: containing free end of the head, to the end position +1
Support negative argument: the reciprocal of the n-th position, in fact, executed or length-n
If the second parameter is omitted, showing the position taken directly from starti to the end.
concat and slice are not directly modify the original array, you must use the new variable reception
Delete / insert / replace the array
splice: delete, insert, replace
Delete: arr.splice (starti, n)
Delete arr starting position in starti n elements
Note: n is the number, irrespective containing free end of the head
splice can return the removed element consisting of a temporary array.
was delete = arr.splice (Startie, n)
Insert: arr.splice (starti, 0, the value 1, value 2, ...)
In the insertion position starti arr value 1, value 2, ..., and the original value after starti position, are shifted backward cis
Note: 0 means do not delete, insert a new value only
Does not support the break array type parameter, if passed in the array, it will form a sub-array
Alternatively: var deletes = arr.splice (starti, n, value 1, value 2, ...)
Starti delete start position of n, then insert the value 1, value 2 starti position.
Note: The number of elements to delete, and insert the number of new worth, do not necessarily coincide.
conca and splicet:
the concat: Excellent: break up the array type parameters
Missing: only at the beginning or end of stitching
splice: Excellent: the insertion position can be specified
Missing: break up the array parameter is not supported