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转载: [How to Remove the Last Character from a String in JavaScript - Mastering JS](https://masteringjs.io/tutorials/fundamentals/remove-last-character#:~:text=Nov 12%2C 2021-,To remove the last character from a string in JavaScript,length - 1)

To remove the last character from a string in JavaScript, you should use the slice() method. It takes two arguments: the start index and the end index. slice() supports negative indexing, which means that slice(0, -1) is equivalent to slice(0, str.length - 1) .

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let str = 'Masteringjs.ioF';
str.slice(0, -1); // Masteringjs.io

# Alternative Methods

slice() is generally easier, however other methods available are substring() and replace() . substring() does not have negative indexing, so be sure to use str.length - 1 when removing the last character from the string. replace() takes either a string or a regular expression as its pattern argument. Using /.$/ as the regular expression argument matches the last character of the string, so .replace(/.$/, '') replaces the last character of the string with an empty string.

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let str = 'Masteringjs.ioF';
str.substring(0, str.length - 1); // Masteringjs.io
str.substr(0, str.length - 1); // Masteringjs.io
str.replace(/.$/, ''); // Masteringjs.io

# Advanced Features

With replace() , you can specify if the last character should be removed depending on what it is with a regular expression. For example, suppose you want to remove the last character only if the last character is a number. You can use .replace(/\d$/, '') as shown below.

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// For a number, use \d$.
let str = 'Masteringjs.io0';
str.replace(/\d$/, ''); // Masteringjs.io

let str2 = 'Masteringjs.io0F';
// If the last character is not a number, it will not replace.
str.replace(/\d$/, ''); // Masteringjs.io0F;

# Comments from MDN

String.prototype.substring() - JavaScript | MDN

# The difference between substring() and substr()

There are subtle differences between the substring() and substr() methods, so you should be careful not to get them confused.

  • The two parameters of substr() are start and length , while for substring() , they are start and end .
  • substr() 's start index will wrap to the end of the string if it is negative, while substring() will clamp it to 0 .
  • Negative lengths in substr() are treated as zero, while substring() will swap the two indexes if end is less than start .

Furthermore, substr() is considered a legacy feature in ECMAScript, so it is best to avoid using it if possible.

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const text = 'Mozilla';
console.log(text.substring(2, 5));  // => "zil"
console.log(text.substr(2, 3));     // => "zil"

# Differences between substring() and slice()

The substring() and slice() methods are almost identical, but there are a couple of subtle differences between the two, especially in the way negative arguments are dealt with.

The substring() method swaps its two arguments if indexStart is greater than indexEnd , meaning that a string is still returned. The slice() method returns an empty string if this is the case.

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const text = 'Mozilla';
console.log(text.substring(5, 2));  // => "zil"
console.log(text.slice(5, 2));      // => ""

If either or both of the arguments are negative or NaN , the substring() method treats them as if they were 0 .

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console.log(text.substring(-5, 2));  // => "Mo"
console.log(text.substring(-5, -2)); // => ""

slice() also treats NaN arguments as 0 , but when it is given negative values it counts backwards from the end of the string to find the indexes.

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console.log(text.slice(-5, 2))   // => ""
console.log(text.slice(-5, -2))  // => "zil"

See the slice() page for more examples with negative numbers.

# Replacing a substring within a string

The following example replaces a substring within a string. It will replace both individual characters and substrings. The function call at the end of the example changes the string Brave New World to Brave New Web .

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// Replaces oldS with newS in the string fullS
function replaceString(oldS, newS, fullS) {
  for (let i = 0; i < fullS.length; ++i) {
    if (fullS.substring(i, i + oldS.length) === oldS) {
      fullS = fullS.substring(0, i) + newS + fullS.substring(i + oldS.length, fullS.length);
    }
  }
  return fullS;
}

replaceString('World', 'Web', 'Brave New World');

Note that this can result in an infinite loop if oldS is itself a substring of newS — for example, if you attempted to replace ‘ World ’ with ‘ OtherWorld ’ here.

A better method for replacing strings is as follows:

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function replaceString(oldS, newS, fullS) {
  return fullS.split(oldS).join(newS);
}

The code above serves as an example for substring operations. If you need to replace substrings, most of the time you will want to use String.prototype.replace() .

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