Can Javascript RegExp do partial case insensitivity?

Question

I want to know if Javascript RegExp has the ability to turn on and off case insensitivity within the regular expression itself. I know you can set the modifier for the entir

Answer 1

You can write the RegExp in case-sensitive "longhand"

/[tT][eE][xX][tT] [tT][oO] [sS][eE][aA][rR][cC][hH] TOP SECRET/
    .test('text to search TOP SECRET');
// true

An alternative approach is two regular expressions, an insensitive one followed by a strict one

function test(str) {
    var m = str.match(/text to search (TOP SECRET)/i);
    return (m || false) && /TOP SECRET$/.test(m[1]);
}

test('text to search TOP SECRET'); // true
test('text to search ToP SECRET'); // false

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Further, function test above can be optimised in this specific case (as the TOP SECRET part is effectively a string literal which will always have exactly the same form), it doesn't require a second full RegExp test to check it, i.e. you can do

(m || false) && 'TOP SECRET' === m[1];