Summary of replace in javascript

ECMAScript provides the replace () method. This method takes two arguments, the first argument can be an RegExp object or a string, and the second argument can be a string or a function. Now let's explain several possible situations in detail.

1. The case where both parameters are strings

 var text = 'cat, bat, sat, fat';
 //  Find in the string at And will at Replace with ond , replace only 1 Times 
 var result = text.replace('at', 'ond');
// "cond, bat, sat, fat"
 console.log(result);

2. The first argument is an RegExp object, and the second argument is a string

We can see that in this case, only the first at is replaced, and if you want to replace all at, you must use the RegExp object.

var text = 'cat, bat, sat, fat';
 //  Use /at/g  Matching in the Global at , and use ond Make a replacement 
 var result = text.replace(/at/g, 'ond');
 // cond, bond, sond, fond
 console.log(result);

3. Consider capturing groups in an RegExp object

RegExp has nine attributes for storing capture groups. $1, $2... $9 for storing matching capture groups 1 through 9, respectively. We can access these properties to get the stored values.

var text = 'cat, bat, sat, fat';
 //  Use /(.at)/g  The parentheses are capture groups, and only 1 Therefore, the matching value is stored in the $1 Medium 
 var result = text.replace(/(.at)/g, '$($1)');
 // $(cat), $(bat), $(sat), $(fat)
 console.log(result);

4. If the second argument is a function, there is no capture group in RegExp object

var text = 'cat, bat, sat, fat';
 //  Use /at/g  Matches all of the at And replace it with ond , 
 //  The parameters of the function are: the current matching character, the position of the current matching character, and the original string 
 var result = text.replace(/at/g, function(match, pos, originalText) {
  console.log(match + ' ' + pos);
  return 'ond'
 });
 console.log(result);
 //  Output 
 /*
  at 1 dd.html:12:9
  at 6 dd.html:12:9
  at 11 dd.html:12:9
  at 16 dd.html:12:9
  cond, bond, sond, fond dd.html:16:5
 */

5. If the second argument is a function, there is a capture group in the RegExp object

var text = 'cat, bat, sat, fat';
 //  Use /(.at)/g  Matches all of the at And replace it with ond , 
 //  When a capture group exists in a regular expression, the parameters of the function 1 Next is: Pattern Matches, 1 The matches of the capture groups, 
 //  No. 1 2 Matches of 10 capture groups ... The position of the match in the string, the original string 
 var result = text.replace(/.(at)/g, function() {
  console.log(arguments[0] + ' ' + arguments[1] + ' ' + arguments[2]);
  return 'ond'
 });
 console.log(result);
 //  Output 
 /*
  cat at 1 
  bat at 6 
  sat at 11 
  fat at 16 
  cond, bond, sond, fond 
 */

These are all possible scenarios for the replace method, and we use replace and regular expressions to implement the string trim method.

(function(myFrame) {
  myFrame.trim = function(str) {
   // ' hello world '
   return str.replace(/(^\s*)|(\s*$)/g, '');
  };
  window.myFrame = myFrame;
 })(window.myFrame || {});
 //  Test 
 var str = ' hello world '
 console.log(str.length); // 15
 console.log(myFrame.trim(str).length); // 11