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Regular expressions - JavaScript | MDN

Using test method

• One way to test a regex is using the .test() method.
• The .test() method takes the regex, applies it to a string (which is placed inside the parentheses), and returns true or false if your pattern finds something or not.

let testStr = "freeCodeCamp";
let testRegex = /Code/;
testRegex.test(testStr); // true

let myString = "Hello, World!";
let myRegex = /Hello/;
let result = myRegex.test(myString); // true

let testStr = "Hello, my name is Kevin.";
let testRegex = /Kevin/;
testRegex.test(testStr); //true

let wrongRegex = /kevin/;
wrongRegex.test(testStr) // false

• If you want to find the word the in the string The dog chased the cat, you could use the following regular expression: /the/
  • Notice that quote marks are not required within the regular expression.

Match a Literal String with Different Possibilities

• Using regexes like /coding/, you can look for the pattern coding in another string.
• This is powerful to search single strings, but it's limited to only one pattern. You can search for multiple patterns using the alternation or OR operator: |.

let catPetString = "James has a pet cat.";
let dogPetString = "James has a pet dog.";
let lionPetString = "James has a pet lion.";
let petRegex = /cat|dog|fish/; 
let test1 = petRegex.test(catPetString ); // true
let test2 = petRegex.test(dogPetString ); // true
let test3 = petRegex.test(lionPetString ); // false

Ignore Case While Matching

• Case (or sometimes letter case) is the difference between uppercase letters and lowercase letters.
• You can match both cases using what is called a flag. There are other flags but here you'll focus on the flag that ignores case - the i flag.

let myString = "freeCodeCamp";
let fccRegex = /freecodecamp/i; // i at the end will flag the regex to ignorecase
let result = fccRegex.test(myString);