How to Escape HTML and JavaScript for Secure Coding?

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Escaping user input is an important step in secure coding to prevent security vulnerabilities like cross-site scripting (XSS). To escape HTML and JavaScript, you need to replace certain characters with their corresponding HTML entities, so that they are treated as literal characters and not as part of the code.

Here’s an example of escaping HTML in JavaScript:

let str = '<h1>Hello, World!</h1>';

str = str.replace(/[&<>"']/g, function(m) {
  return {
    '&': '&',
    '<': '<',
    '>': '>',
    '"': '"',
    "'": '''
  }[m];
});

console.log(str); // Output: '<h1>Hello, World!</h1>'

In this example, the .replace() method is called on the string str. The first parameter to the method is a regular expression that matches the characters &, <, >, ", and '. The second parameter is a function that takes the matched character as its argument and returns the corresponding HTML entity. This function uses an object literal to map characters to entities.

The g flag in the regular expression makes the .replace() method perform a global search, so all occurrences of the characters are replaced.

For JavaScript, you need to escape characters that have special meaning in JavaScript. For example, you need to escape single quotes ' and newline characters \n. Here’s an example:

let str = "Hello, 'world'!";

str = str.replace(/'/g, "\\'");

console.log(str); // Output: "Hello, \\'world\\'!"

In this example, the .replace() method is called on the string str. The first parameter to the method is a regular expression that matches the single quote character '. The second parameter is a string that replaces the matched character with a string that contains two characters: a backslash \ and a single quote '. The backslash is used to escape the single quote, so that it is treated as a literal character and not as the end of the string.

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