src/string-to-integer-atoi/res.js

/**
 * res.js
 * @authors Joe Jiang (hijiangtao@gmail.com)
 * @date    2017-04-03 22:44:48
 *
 * Problem: Implement atoi to convert a string to an integer.
 * 
 * @param {string} str
 * @return {number}
 */
let myAtoi = function(str) {
	const INT_MAX = 2147483647,
		INT_MIN = -2147483648,
		bound = Number.parseInt(INT_MAX / 10);
	let strlen = str.length,
		signal = 1, // 1 stands for positive number, 0 stands for negative number
		res = 0;

	while (str[0] && str[0] === ' ') {
		str = str.slice(1);
		strlen -= 1;
	}

	if (strlen === 0) {
		return 0;
	}

	if (str[0] === '-') {
		signal = 0;
		str = str.slice(1);
	} else if (str[0] === "+") {
		str = str.slice(1);
	}

	while (str[0] >= '0' && str[0] <= '9') {
		//   console.log(str[0]);
		let element = Number.parseInt(str[0]);

		if (res > bound || (res === bound && element > 7)) {
			if (signal) {
				return INT_MAX;
			}
			return INT_MIN;
		}

		res = res * 10 + element;
		str = str.slice(1);
	}

	return signal ? res : -res;
};