I want to make code that converts uppercase and lowercase in JavaScript.
For example, 'Hi, Stack Overflow.' → 'hI, sTACK oVERFLOW'
How can I do it?
- did you try something ?kevin ternet– kevin ternet2016-10-22 12:43:03 +00:00Commented Oct 22, 2016 at 12:43
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6 Answers
You could run over each character, and then covert it to lowercase if it's in uppercase, to uppercase if it's in lowercase or take it as is if it's neither (if it's a comma, colon, etc):
str = 'Hi, Stack Overflow.'; res = ''; for (var i = 0; i < str.length; ++i) { c = str[i]; if (c == c.toUpperCase()) { res += c.toLowerCase(); } else if (c == c.toLowerCase()) { res += c.toUpperCase(); } else { res += c; } } 
2 Comments
Christian Zosel
See also this answer for a little more advanced solution: stackoverflow.com/a/38703925/1743938
Ivan Sieder
It's generally not considered mutating a string directly (by accessing it's index). It's usually preferred to convert it to an array (using .split() without any parameter), then iterate over the array and reassemble the string with .join(). Just as an idea.
You can try this simple solution using map()
var a = 'Hi, Stack Overflow!' var ans = a.split('').map(function(c){ return c === c.toUpperCase() ? c.toLowerCase() : c.toUpperCase() }).join('') console.log(ans)Comments
<!DOCTYPE html> <html> <head> <title>hello</title> <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script> </head> <body> <script> $(document).ready(function(){ var x = 'Hi, Stack Overflow.'; alert(caseAlter(x)); function caseAlter(txt){ var output = ""; for(var i = 0; i < txt.length; i++){ if(txt[i] == txt[i].toUpperCase()){ output += txt[i].toLowerCase(); }else{ output += txt[i].toUpperCase(); } } return output; } }); </script> </body> </html> 
Comments
A function which will do this for you (also at CodePen):
function reverseCase(input) { var output = [] for(var char in input) { var character = input[char] if(character == character.toUpperCase()) output.push(character.toLowerCase()) else output.push(character.toUpperCase()) } return output.join('') } 
1 Comment
Peter Mortensen
The CodePen link is broken (404).
var input = 'Hi, Stack Overflow.' var arr = input.split(' '); alert(arr); var output = arr.map(function(elem){ return (elem[0].toLowerCase() + elem.substring(1,elem.length).toUpperCase()); }); alert(output.join()); 
Comments
var hi = 'Hi, Stack Overflow.'; var hI = hi.split(""); for(var i=0; i<hI.length; i++) { if(hI[i] == hI[i].toLowerCase()) hI[i] = hI[i].toUpperCase(); else if(hI[i] == hI[i].toUpperCase()) hI[i] = hI[i].toLowerCase(); } hI = hI.join(""); alert(hI); //'hI, sTACK oVERFLOW'