`join（）`和多维数组Javascript

Question

I have this code:

var arr = str.split(' ');
for(var i=0,  l=arr.length; i<l; i++) {
    arr[i].split('');
    arr[i][0].toUpperCase();
    almost =arr[i].join('');
}

It returns the error " arr[i].join is not a function". I assume I have something wrong with the data types but I have no idea how to fix it.

Answer 1

When you use arr[i].split() you are not changing original element in array, so when you use arr[i].join('') you get error because arr[i] is still just a string and you can't use join on string. Instead you need to assign new value to that element so your code should look like this.

 var arr = 'lorem ipsum'.split(' '); for (var i = 0, l = arr.length; i < l; i++) { arr[i] = arr[i].split(''); arr[i][0] = arr[i][0].toUpperCase(); arr[i] = arr[i].join(''); } console.log(arr.join(' ')) 

Or instead you can store that value in variable, change it and then set it to value of current element in loop.

 var arr = 'lorem ipsum'.split(' '); for (var i = 0, l = arr.length; i < l; i++) { var e = arr[i].split(''); e[0] = e[0].toUpperCase(); arr[i] = e.join('') } console.log(arr.join(' ')) 

Answer 2

Here, I think this is what you're looking for:

var str = 'This is a test string';

var arr = str.split(' ');
for(var i=0,  l=arr.length; i<l; i++) {
    var word = arr[i].split('');
    word[0] = word[0].toUpperCase();
    arr[i] = word.join('');
}
console.log(arr.join(' '));

JSFiddle: https://jsfiddle.net/6f9yoqtg/1/

Answer 3

It looks like others have explained why join does not work on a string. However, I noticed that your goal seems to be to uppercase every word in str . You can use the String#replace method for that, taking a function as the section parameter.

 var string = 'word word words things amazing icons yup' console.log(string) string = string.replace(/(\\S)(\\S*)/g, function (_, first, rest) { return first.toUpperCase() + rest }) console.log(string) 

Answer 4

With ES6, you could use destructuring ans rest syntax.

 var str = 'This is a test string'; str = str.split(' ').map(([first, ...rest]) => [first.toUpperCase(), ...rest].join('')).join(' '); console.log(str); 

Answer 5

There are a few concepts that you need to consider here. if I'm not mistaken you are trying to create a function that will capitalize each first letter in a given string.

Start by simply creating a function that will take any string as a parameter using the variable str and then later manipulate it. Think of the function as a funnel something goes into it and then we have something that will come out the other end as an output. make sure you call the function later.

  function capitalize(str) { };
capitalize(every firSt lettEr of the sentence);

Now inside the curly brackets is where the magic happens. we can use the .toLowerCase(), in case we might have capital letters some where along the string, and then use the .split() to split apart the letters at every empty space if there are many words in the string that we are trying to capitalize. Remember that after the split() you will no longer have a string but rather a string inside an array. Note that if you use 2 empty spaces in the split(' '), you will only capitalize the very first letter of the sentence.

function capitalize(str) { str = str.toLowerCase().split(' '); return str;}
//call function 
capitalize(every firSt lettEr of the sentence);
//outputs ["every first letter of the sentence"]

then to iterate through each word in the array using a simple for loop like you have that will look like this:

for (var i=0; i<str.length; i++){}

in the curly brackets of the loop you will want to add a statement that will take the first letter of each word capitalize it then add the rest of the letters using splice(). it will go through each word in the array until there are non left, which is why we used the str.length. Lastly you will use the str.join() to put together the all the words in the array, that had a space between them, back into a string. it will look like this:

function titleCase(str) {
  str = str.toLowerCase().split(' ');
  for (var i = 0; i < str.length; i++) {
    str[i] = str[i].charAt(0).toUpperCase() + str[i].slice(1); 
}

  return str.join(' ');
}
capitalize("every firSt lettEr of the sentence");

//output "Every First Letter Of The Sentence"

I hope that helped. if you need any help with the concepts don't be afraid to ask.