LastIndex property of the regular

 

Description: The next match of the regular starting position for the lastIndex property provisions.

Note:  This property is only set to use the g flag.

Results are matched by the process of the last RegExp.exec () and RegExp.test () found, they are referred to the position as a starting point lastIndex property next retrieval. Thus, by repeatedly call these two methods through which all matches a text string.

Note: This property is readable and writable. As long as the next target string of beginning a search, you can set it up. When the method exec () or test () could not find a match text, they will automatically reset to 0 lastIndex property.

　　Example 1: Try the global string substring "ain", and outputs the match after the completion of the lastIndex property:

var str="The rain in Spain stays mainly in the plain";
var patt1=/ain/g;

while (patt1.test(str)==true) 
{
    document.write("'ain' found. Index now at: "+patt1.lastIndex);
    document.write("<br>");
};

　　Example 2: repeatedly retrieve and print out the lastIndex position, when finally retrieved not retrieved it from scratch in line with the retrieval

var str="The rain in Spain stays";
var patt=/ain/g;
console.log(patt.test(str))//true
console.log(patt.lastIndex)//8
console.log(patt.test(str))//true
console.log(patt.lastIndex)//17
console.log(patt.test(str))//false
console.log(patt.lastIndex)//0
console.log(patt.test(str))//true
console.log(patt.lastIndex)//8

　　Example 3: How to avoid caused due lastIndex bug: always create a new RegExp can avoid this problem

var str="The rain in Spain stays";
console.log(/ain/g.test(str))//true
console.log(/ain/g.lastIndex)//0
console.log(/ain/g.test(str))//true
console.log(/ain/g.lastIndex)//0
console.log(/ain/g.test(str))//false
console.log(/ain/g.lastIndex)//0
console.log(/ain/g.test(str))//true
console.log(/ain/g.lastIndex)//0