JavaScript toUpperCase 不起作用。 为什么？

Question

I am doing a simple function. To turn all words first-letter to upper case, but It simply doesn't work, neither display any errors:

 function formatTitle(input) { var words = input.split(' '); for (var i = 0; i < words.length; i++) { words[i][0] = words[i][0].toUpperCase(); }; return words.join(' '); }; var newTitle = formatTitle("all words first-letter should be upper case"); document.write(newTitle);

Thanks in advance.

Answer 1

The problem is that strings in javascript are immutable. You can't just change a char like this.

A solution would be this:

words[i] = words[i][0].toUpperCase()+words[i].slice(1);

But you could have a simpler and faster code using a regular expression:

return input.replace(/\b\w/g,function(b){ return b.toUpperCase() })

(here with a more complete uppercasing, not just after spaces - if you want to stick to spaces use replace(/(\\s+|^)\\w/g,function(b){ return b.toUpperCase() }) )

Answer 2

Problem

Because

words[i][0] = 'something'

does not update the words[i] .

Problem Demo

 var myVar = 'abc'; myVar[0] = 'd'; document.write(myVar); // abc

Solution

You can use substr to get the first character and update the value of whole string.

Solution Demo

 function formatTitle(input) { var words = input.split(' '); for (var i = 0; i < words.length; i++) { words[i] = words[i].substr(0, 1).toUpperCase() + words[i].substr(1); } return words.join(' '); } var newTitle = formatTitle("all words first-letter should be upper case"); document.write(newTitle);

Answer 3

How wrote Denis the reason is that strings in javascript are immutable (numbers and booleans are also immutable).

Another very simple solution for Upperize the first char of a string is:

function firstUpper(word) {
     return word.charAt(0).toUpperCase() + word.substring(1);
};

I suggest also to read this post: Understanding Javascript immutable variable

Hope this help