Create a Regular Expression

// Regular Expression Literal 
const regexObj = /^word$/

// Regular Expression Constructor
const regexObj = new RegExp("^word$");

Test & Replace

Test example

const regex = /^corn/;

regex.test('corncob')
true
regex.test('popcorn')
false

Replace example

const regex = /^corn/;
const string1 = 'corndog'
string1.replace(regex, 'hot')
'hotdog'

const string2 =  'popcorn'
string2.replace(regex, 'tart')
'popcorn'

Flags

i Case-insensitive
g Global; keeps searching for the regex
m Multiline; considers the line break a part of the word

Usage
/regex/igm

Case-insensitive flag example

/lion/i.test('LION');
> true
'LION'.replace(/lion/i, 'mouse');
> "mouse"

Global flag example

'She ate a watermelon at the waterpark.'.replace(/water/, '');
> "She ate a melon at the waterpark."

'She ate a watermelon at the waterpark.'.replace(/water/g, '');
> "She ate a melon at the park."

Multiline flag example

const treat = `cheese
cheese
cheese`;

treat.replace(/^cheese$/, 'fruit');
cheese
cheese
cheese

treat.replace(/^cheese$/m, 'fruit');
fruit
cheese
cheese

treat.replace(/^cheese$/mg, 'fruit');
fruit
fruit
fruit