A brief discussion on the magic of parseInt() in JavaScript

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The reason for writing this blog is that I was doing the daily question of Leetcode today. It is a question about converting a string to an integer (atoi). If you are interested, you can click on the title to see the detailed description. After I debugged it many times and finally submitted it successfully, I went to the comment section to see the experts' solutions. After reading it, I couldn't help but sigh that parseInt() in JavaScript is so excellent. This tells me a truth: the APIs that we think we are very familiar with may not be truly mastered by us. ”

My answer

/**
 * @param {string} str
 * @return {number}
 */
var myAtoi = function(str) {
    str = str.trim();
    //Intercept the first character of the string var firstChar = str.charAt(),res = '',regSymbol = /^[\-\+]{1}/,regNumber = /^[0-9]{1}/;

    if(!regSymbol.test(firstChar) && !regNumber.test(firstChar)){
        return 0;
    }

    //The first character is + or -
    if(regSymbol.test(firstChar)){
        var sliceStr = str.slice(1,str.length);
        for(var i=0;i<sliceStr.length;i++){
            if (regNumber.test(sliceStr.charAt(i))) {
                res += sliceStr.charAt(i);
            }else{
                break;
            }
        }
        
        (res.length) ? res = parseInt(firstChar + res) : res = 0;

        if(firstChar == '-' && res < Math.pow(-2,31)){
            res = Math.pow(-2,31);
        }

        if(firstChar == '+' && res > Math.pow(2,31) - 1){
            res = Math.pow(2,31) - 1;
        }

        return res;
    }

    //The first character is a number if (regNumber.test(firstChar)) {
        var sliceStr = str;
        for(var i=0;i<sliceStr.length;i++){
            if (regNumber.test(sliceStr.charAt(i))) {
                res += sliceStr.charAt(i);
            }else{
                break;
            }
        }

        if (parseInt(res) > Math.pow(2,31) - 1) {
            res = Math.pow(2,31) - 1;
        }

        return res;
    }
};

The answer from the boss

/**
 * @param {string} str
 * @return {number}
 */
var myAtoi = function(str) {
    const number = parseInt(str, 10);

    if(isNaN(number)) {
        return 0;
    } else if (number < Math.pow(-2, 31) || number > Math.pow(2, 31) - 1) {
        return number < Math.pow(-2, 31) ? Math.pow(-2, 31) : Math.pow(2, 31) - 1;
    } else {
        return number;
    }
};

By comparison, we know that parseInt() in JavaScript has performed a series of operations such as intercepting empty strings, judging the first letter, and returning number type results. It just happens to be a perfect match for today's daily question. It's so cool to use parseInt() to solve this problem.

This is the end of this article about the wonderful uses of parseInt() in JavaScript. For more relevant JavaScript parseInt() content, please search 123WORDPRESS.COM’s previous articles or continue to browse the following related articles. I hope everyone will support 123WORDPRESS.COM in the future!

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