JavaScript parseInt not working with "10"?

Question

I wrote the function that tokenizes arithmetic string expression into an array of tokens, such as numbers and operators. Everything's fine but I get a weird results when dealing with strings containing "10". Here's the code:

function tokenizeString(expressionString) {
    const tokenArray = [];

    let token = "";
    for (let i = 0; i < expressionString.length; i++) {
        if (parseInt(expressionString[i])) {
            token += expressionString[i];
        } else {
            tokenArray.push(parseInt(token));
            token = "";
            tokenArray.push(expressionString[i]);
        }
    }

    if (token !== "") {
        tokenArray.push(parseInt(token));
    }

    return tokenArray;
}

console.log(tokenizeString("14+2/8")); // [14, "+", 2, "/", 8]
console.log(tokenizeString("10+1")); // [1, '0', NaN, '-', 3] ??

For now I can't come up with an idea, why this happens.

because 0 is falsy. `parseInt(expressionString[i] is false when 0` — cmgchess, Feb 12 '22 at 08:01
@cmgchess Thank you! It works, I forgot about JS falsy values :) — tnsaturday, Feb 12 '22 at 08:04
[How to debug small programs](https://ericlippert.com/2014/03/05/how-to-debug-small-programs/) and [What is a debugger and how can it help me diagnose problems?](https://stackoverflow.com/q/25385173) — VLAZ, Feb 12 '22 at 08:07

score 1 · Answer 1 · answered Feb 12 '22 at 08:07

Instead of parseInt in the if(parseInt(expressionString[i])){} you could use isNaN() to check if the string is number or not isNaN() returns true if not a number so your if would be if (!isNaN(expressionString[i])){}

function tokenizeString(expressionString) {
    const tokenArray = [];

    let token = "";
    for (let i = 0; i < expressionString.length; i++) {
        if (!isNaN(expressionString[i])) {
            token += expressionString[i];
        } else {
            tokenArray.push(parseInt(token));
            token = "";
            tokenArray.push(expressionString[i]);
        }
    }

    if (token !== "") {
        tokenArray.push(parseInt(token));
    }

    return tokenArray;
}

console.log(tokenizeString("14+2/8")); // [14, "+", 2, "/", 8]
console.log(tokenizeString("10+1")); // [10, '+', 1] ??

JavaScript parseInt not working with "10"?

1 Answers1