无法将 null 分配给变量

Question

 const letsMatch = (string, char) => { const newRegex = new RegExp(char, "gi"); let result = string.match(newRegex); const findNegIndex = result.indexOf(char); if (findNegIndex === null) { return result = 0; } else { if (result.length === 2) { const findFirstIndex = fiveT.indexOf(char); const findSecondIndex = fiveT.indexOf(char, findFirstIndex + 1); result = findSecondIndex - findFirstIndex + 2; return result; } else { return (result = 0); } } } console.log(letsMatch('totititiTo', 'r'))

line 4: const findNegIndex = result.indexOf(char); Throws Uncaught TypeError: Cannot read properties of null (reading 'indexOf').

Answer 1

According to the documentation , String.prototype.match() will return null ( not an empty array) when no matches are found.

And no matches are found.

You can default to an empty array when it returns null :

 const letsMatch = (string, char) => { const newRegex = new RegExp(char, "gi"); let result = string.match(newRegex) || []; // here const findNegIndex = result.indexOf(char); if (findNegIndex === null) { return result = 0; } else { if (result.length === 2) { const findFirstIndex = fiveT.indexOf(char); const findSecondIndex = fiveT.indexOf(char, findFirstIndex + 1); result = findSecondIndex - findFirstIndex + 2; return result; } else { return (result = 0); } } } console.log(letsMatch('totititiTo', 'r'))

(As an aside, it's not really clear what this function is meant to accomplish, or what you expect return result = 0 to mean other than return 0 . But at the very least the error is because you're assuming string.match will always return an array, and there exists a use case where it does not.)

Answer 2

Depending on what you're coding in...

Use?. - it'll return undefined if result doesn't have that property, and the || will shunt it on over to the null const findNegIndex = result?.indexOf(char) || null; const findNegIndex = result?.indexOf(char) || null;

or

const findNegIndex = result? result.indexOf(char): null;

I'd also shy away from a variable named "string", for readability's sake - since String.match