JavaScript: Pad (left, right) a string to get to a determined length

JavaScript String: Exercise-20 with Solution

Pad String to Length

Write a JavaScript function that can pad (left, right) a string to get to a specific length.

Test Data:
console.log(formatted_string('0000',123,'l'));
console.log(formatted_string('00000000',123,''));
Output:
"0123"
"12300000"

Visual Presentation:

Sample Solution:

JavaScript Code:

// Define a function named formatted_string with three parameters: pad, user_str, and pad_pos
function formatted_string(pad, user_str, pad_pos) {
  // Check if user_str is undefined, if so, return pad
  if (typeof user_str === 'undefined') 
    return pad;
  // Check if pad_pos is 'l' (left), if true, execute the following block
  if (pad_pos == 'l') {
    // Concatenate pad with user_str, slice the result to keep only the last characters equal to the length of pad, and return the result
    return (pad + user_str).slice(-pad.length);
  } 
  // If pad_pos is not 'l', execute the following block
  else {
    // Concatenate user_str with pad, then substring to keep only the characters equal to the length of pad, and return the result
    return (user_str + pad).substring(0, pad.length);
  }
}
// Test the function with different parameters and log the results to the console
console.log(formatted_string('0000',123,'l'));
console.log(formatted_string('00000000',123,''));

Output:

0123
12300000

Explanation:

The above JavaScript code defines a function "formatted_string()" that takes three parameters: 'pad', 'user_str', and 'pad_pos'. Here's a brief explanation -

• The function checks if 'user_str' is 'undefined'. If so, it returns 'pad'.
• If 'pad_pos' is 'l' (indicating left padding), it concatenates 'pad' with 'user_str', keeps only the last characters equal to the length of 'pad', and returns the result.
• If 'pad_pos' is not 'l', it concatenates 'user_str' with 'pad', keeps only the characters equal to the length of 'pad', and returns the result.

Flowchart:

Live Demo:

See the Pen JavaScript Pad (left, right) a string to get to a determined length - string-ex-20 by w3resource (@w3resource) on CodePen.

Improve this sample solution and post your code through Disqus.

Previous: Reverse a Binary string.
Next: Repeat a string a specified times.