如何在不使用 javascript 中的替换函数的情况下替换字符串？

Question

I'm trying to create a javascript program where I replace all spaces in a string with %20 without using the replace function. I'm getting an error when I try to run my program. Not sure what's wrong.

 let urlEncode = function(text) { text = text.trim(); let newstring; for (let i = 0; i < text.length; i++) { if (text[i] == " ") { newstring[i] = "%20"; } else { newstring[i] = text[i]; } } return newstring; }; console.log(urlEncode("blue is greener than purple for sure"));

Answer 1

Strings are immutable - you can't assign to their indicies. Rather, initialize newstring to the empty string, use += to concatenate the existing string with the new character(s):

 let urlEncode = function(text) { text = text.trim(); let newstring = ''; for (const char of text) { newstring += char === ' '? '%20' : char; } return newstring; }; console.log(urlEncode("blue is greener than purple for sure"));

Or, don't reinvent the wheel, and use encodeURIComponent :

 console.log(encodeURIComponent("blue is greener than purple for sure"));

Answer 2

You can use combination of split and join to achieve in simplified way.

 let urlEncode = function(text) { return text .trim() .split(" ") .join("%20"); }; console.log(urlEncode("blue is greener than purple for sure"));

Answer 3

Your Error Is first you must set newstring in first let only create your variable but not assign any value to it then newstring[0] is undefined then you get error i use += for add char to string and it is better
you can change your Code Like this

 let urlEncode = function(text) { text = text.trim(); let newstring=""; for (let i = 0; i < text.length; i++) { if (text[i] == " ") { newstring+= "%20"; } else { newstring+= text[i]; } } return newstring; }; console.log(urlEncode("blue is greener than purple for sure"));