How do you check if a string contains only letters and numbers in javascript?

1. The RegExp test[] Method

To check if a string contains only letters and numbers in JavaScript, call the test[] method on this regex: /^[A-Za-z0-9]*$/. If the string contains only letters and numbers, this method returns true. Otherwise, it returns false.

function onlyLettersAndNumbers[str] {
  return /^[A-Za-z0-9]*$/.test[str];
}const str1 = 'number60';
const str2 = 'contains spaces';
const str3 = 'has special characters !@#$%^&';console.log[onlyLettersAndNumbers[str1]]; // true
console.log[onlyLettersAndNumbers[str2]]; // false
console.log[onlyLettersAndNumbers[str3]]; // false

The RegExptest[] method searches for a match between the regular expression and a specified string.

The / and / characters are used to start and end the regular expression.

The ^ character matches the beginning of the string, while the $ character matches the end of the string.

The square brackets [[]] are used to match any one of multiple specified patterns. In our example, we specify three patterns: A-Z, a-z, and 0-9.

A-Z matches any uppercase letter.

a-z matches any lowercase letter.

0-9 matches any digit.

The * character matches zero or more occurrences of a particular pattern. We add it after the square brackets to match any of the patterns in the brackets as many times as possible.

2. The String match[] Method

We can use the String match[] method in place of RegExp test[].

function onlyLettersAndNumbers[str] {
  return Boolean[str.match[/^[A-Za-z0-9]*$/]];
}const str1 = 'number60';
const str2 = 'contains spaces';
const str3 = 'has special characters !@#$%^&';console.log[onlyLettersAndNumbers[str1]]; // true
console.log[onlyLettersAndNumbers[str2]]; // false
console.log[onlyLettersAndNumbers[str3]]; // false

The String match[] method returns an array of all the matches of a regular expression in a string. If there are no matches, it returns null.

const str1 = 'number60';
const str2 = 'contains spaces';
const str3 = 'has special characters !@#$%^&';// [ 'number60', index: 0, input: 'number60', groups: undefined ]
console.log[str1.match[/^[A-Za-z0-9]*$/]];console.log[str2.match[/^[A-Za-z0-9]*$/]]; // null
console.log[str3.match[/^[A-Za-z0-9]*$/]]; // null

We pass the result of match[] to the Boolean constructor to convert it to a Boolean. Boolean[] converts truthy values to true, and falsy values to false.

In JavaScript, there are six falsy values: undefined, null, NaN, 0, '' [empty string], and false. Every other value is truthy.

console.log[Boolean[undefined]]; // false
console.log[Boolean[['number60']]]; // true
console.log[Boolean[null]]; // false
console.log[Boolean[5]]; // true

Removing Letters and Numbers from a String

If you would like to remove any letters and numbers from the string, you can use the String replace[] method.

function removeLettersAndNumbers[str] {
  return str.replace[/[A-Za-z0-9]/g, ''];
}const str1 = 'number!60 ?';
const str2 = '#wel_com%e';console.log[removeLettersAndNumbers[str1]]; // ! ?
console.log[removeLettersAndNumbers[str2]]; // #_%

The String replace[] method returns a new string with some or all matches of a specified pattern replaced by a replacement. We use an empty string [''] as the replacement to have all the letters and numbers removed in the resulting string.

We use the g [global] flag to match all the occurrences of the pattern in the string. If we don't specify this flag, only the first match of a letter or number will be removed.

function removeLettersAndNumbers[str] {
  // 'g' flag not set
  return str.replace[/[A-Za-z0-9]/, ''];
}const str1 = 'number!60 ?';
const str2 = '#wel_com%e';console.log[removeLettersAndNumbers[str1]]; // umber!60 ?
console.log[removeLettersAndNumbers[str2]]; // #el_com%e

Updated at: codingbeautydev.com

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