Javascript Regular Expression :Negative Look Ahead

Negative lookahead is achieved with the (?!) syntax, which behaves like

(?=). It matches the previous item only if the expression contained in (?!)

does not immediately follow.

Code:

var line ="USD 100 USD 350 USD 345.56 USD currency USD rate"

var pattern=/USD(?!\s\d+\.{0,}\d+)/gm

var result = line.match(pattern)

console.log(result)

var lastIndex

while ((match = pattern.exec(line))) {

lastIndex = match.index;

console.log("Occurance At:" + lastIndex)

}

Output:

[ 'USD', 'USD' ]

Occurance At:27

Occurance At:40

Explanation:

This regex will match all USD words not followed by a number.

In this case one followed by 'currency' word & other followed vy 'rate' word.