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Primary LanguageJavaScriptOtherNOASSERTION

String Repetition & Searching in JavaScript

Learning Goals

  • Demonstrate string repitition in JavaScript
  • Demonstrate searching in JavaScript
  • Use repeat() to duplicate strings
  • Declare a function that utilizes search() method

Introduction

Working with String values is one of the most popular functions in JavaScript. Strings are objects in the JavaScript language, and working with their values is one of the most common tasks a JavaScript developer performs. We have various functions that provide ways to access or manipulate the contents of a string such as with repitition and searching.

Demonstrate String Repitition in JavaScript

Ever needed to repeat a string or character multiple times? If not, think of a scenario such as a song with lyrics that is repeated over and over again. There have been a number of complex ways to do such a simple operation with loops, but now repeat() is available in JavaScript!

Manual String Repitition

Even though we can now leverage the repeat() method that has been added to the ECMAScript 2015 specification, it may not be available in all implementations yet. It will be useful to know how to write a simpler version of the function manually.

The most scaled down implementation of a repeater function without loops and conditionals looks like this:

function repeat(str, num) {
  return (new Array(num+1)).join(str); 
}

repeat("foo",3)
//=> "foofoofoo"

String Repitition With JavaScript's repeat() Method

The repeat() method constructs and returns a new string which contains the specified number of copies of the string on which it was called. It's just a couple of lines:

"foo".repeat(3)
//=> "foofoofoo"

Demonstrate Searching in JavaScript

Knowing if something is or isn't in a string can be very important. When you want to know whether a pattern is found in a string use search(). search() method executes the search for a match between a String or a regular expression and the search String. In JavaScript, a regular expression is used to match character combinations in strings.

This method searches the string for the specified value and returns its position of the match. The search value can be the string or the regular expression. The search method returns -1 if no match is found.

let str = 'Obama was the 44th president of the US';
let result  = str.search('44th');
console.log(result);
// => 14

Use repeat() to Duplicate Strings

Let's put repeat() to the test! "Hey Jude" is a song by English rock band the Beatles and it was named the 10th "biggest" song of all time by Billboard. After the fourth verse in this song, the same lyrics are repeated for more than four minutes. The popularity of the "long-play" (LP) record started to pick up in the 1960s, and performers took advantage of the longer playing time to create coherent themes or concept albums. It is believed that the Beatles simply wanted to make the song long enough to utilize the entire record.

  • Create a function called heyJude that repeats the lyric "Na na na na na na na, na na na na, hey Jude." 16 times.

Declare a Function that Utilizes the search() Method

We have an online forum and don't want people to be able to create usernames that include swear words or other offensive language. Let's use the search() method to find inappropriate words in usernames and reject them if any are found.

When creating a regular expression, it must be surrounded with slashes: /regular expression/. With that knowledge a search string with the word "pinapplepizza" is inside it looks like this:

let myRegExp = /pinapplepizza/;
  • Create a function called prohibitedLanguage that will prevent usernames with the Strings "candycorn" and/or "brusselssprouts"

Note: A tool in regular expressions is the pipe character | (the pipe character that shares the backslash \ key on standard keyboards) which allows you to search for alternative words /RegExp1|RegExp2/. Instead of just searching for just one word, we can use the pipe character to search for multiple words.

Conclusion

Strings are a fundamental part of every programming language, and JavaScript has many powerful built-in functions that make working with strings easier. The repeat() method simply repeats your string. It returns a new string that concatentates the specified number of copies you indicated. With repeat(), so we no longer have to build up the string some other way. When we want to quickly search a specified pattern and return its index, we can use search() with a String or regular expression, which allows us to match neary any string/phrase.

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