Let’s talk about JavaScript replacement and overwriting

In recent years, JavaScript has become one of the most widely used programming languages ​​in the Internet world. Its powerful functions and easy-to-use features make many people choose to use JavaScript to develop their own web applications.

In JavaScript, string processing is a very common task, and one of the very basic tasks is replacement and overwriting. Whether it is to handle form input or to implement various operations by manipulating strings, the skills of substitution and overwriting are necessary in JavaScript.

In order to help beginners quickly master these two important skills, this article will introduce the replacement and overwriting functions in JavaScript, and how to use these functions to complete various tasks.

1. Replacement

In JavaScript, string replacement can be achieved by using the replace() function. The syntax of this function is as follows:

string.replace(searchValue, replaceValue)

Among them, searchValue represents the string that needs to be replaced, and replaceValue represents the new string used to replace searchValue. For example, we can use the following code to replace all "a" characters in a string with "b":

var str = "abcdaefg";
var newStr = str.replace(/a/g , "b");
console.log(newStr);

In the above code, "bbcdbefg" will be output, indicating that all "a" characters in the string have been successfully replaced with " b".

In addition, the replace() function can also accept a callback function as the second parameter, allowing for more flexible replacement operations. For example, the following code can replace each character of the string in ASCII code:

var str = "abcdaefg";
var newStr = str.replace(/./g, function (match) {
return match.charCodeAt(0).toString();
});
console.log(newStr);

In the above code, " 979899100979710102", indicating that each character in the string has been replaced with its ASCII code.

It is worth noting that the replace() function does not change the original string itself, but generates a new string. Therefore, if you need to save the replacement result, you need to use a new variable to save it.

2. Overwriting

In JavaScript, string overwriting can be achieved by using the substr() and substring() functions. The syntax of these two functions is as follows:

string.substr(startIndex, length)
string.substring(startIndex, endIndex)

Among them, startIndex represents the starting position of the overwritten string , length indicates the length that needs to be covered. The difference between these two functions is that the second parameter in the substring() function indicates the end position of the overwritten string, not the length.

For example, the following code can overwrite the first character in the string to "X":

var str = "abcde";
var newStr = "X" str. substr(1);
console.log(newStr);

In the above code, "Xbcde" will be output, indicating that the first character in the string has been successfully overwritten as "X" .

In addition, the substring() function can also accept a negative number as a parameter, thereby enabling the function of intercepting from the end of the string. For example, the following code overwrites the last character in a string to "Y":

var str = "abcde";
var newStr = str.substring(0, str.length - 1) "Y";
console.log(newStr);

In the above code, "abcde" will be output, indicating that the last character in the string has been successfully overwritten as "Y".

Summary

In JavaScript, replacement and overwriting are very common operations. By using the functions replace(), substr() and substring(), we can easily implement replacement and overwriting operations in strings. Coupled with the callback function we mentioned earlier, we can also handle various situations in strings more flexibly.

Of course, in order to truly master these skills, we still need to continue to practice and try. I believe that in the process of writing JavaScript code, these techniques will help us complete tasks more efficiently, and will also make our code more elegant and easier to maintain.

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