如何用for循环使数组中的字符串复数？

Question

The goal of the challenge I'm currently working on is to take an array and add an 's' onto the end of each element of it (hopefully pluralizing each word).

Here's what I was able to come up with, but I'm certain that I'm not doing this correctly:

var pets = ['dog', 'cat', 'rat'];
for (pets[i] = pets[i] + 's';);
console.log(pets);

I realize I'm probably not all that close to the answer, but this lesson is throwing in a few tips without explaining how/why they work. The entire line of pets[i] = pets[i] + 's'; was what was suggested by the lesson.

I'm hoping to still be able to solve the answer on my own, so if someone could include an explanation as to why the for loop is structured the way you happen to structure it, that would be fantastic!

Answer 1

Classic use case for Array#map

 var pets = ['dog', 'cat', 'rat']; var pluralVersion = pets.map(function(el) { return el + 's'; }); console.log(pluralVersion); 

But, going with your approach, set the new value for each item in array in a for-loop

 var pets = ['dog', 'cat', 'rat']; for (var i = 0, length = pets.length; i < length; i++) { pets[i] = pets[i] + 's'; } console.log(pets); 

Answer 2

Your for syntax is not correct - it should have three parts, like so:

var pets = ['dog', 'cat', 'rat'];
for (var i = 0; i < pets.length; i++) {   //Initialize i as 0. As long as i is less than the length of items in 'pets', continue looping. With each loop, increment i by 1.
   pets[i] = pets[i] + 's';
}
console.log(pets);

Answer 3

In modern Javascript that makes the idea of immutability very popular, you don't actually change values inside your original array but instead map a function to these values and receive a new array. It's as easy as

const pets = ['dog', 'cat', 'rat'];
const petsPlural = pets.map(pet => `${pet}s`);

It may overwhelm you so let's deconstruct each part.

First, the map . This is a property of every array and is a function. When you apply it, you supply a single argument which is, again, a function which is applied to every element in original array one by one. As a result, the return value of calling someArray.map is a new array. The coolest thing is that original array (in your case, pets ) doesn't get changed. It preserves original values!

Next, the (...) => ... syntax. It is an arrow function which has been introduced in ES6 and is already supported by most modern browser (not Safari). For example,

(arg1, arg2) => arg1 + arg2

is a short notation for

function (arg1, arg2) {
  return arg1 + arg2
}

And finally, that backtick thing. It is called template literal . Everything that is enclosed in ${ and } within this string is evaluated while whatever is outside is just places as is. In fact, when you write, say

`${abc}def${123}xyz`

it is equivalent to

abc + 'def' + 123 + 'xyz'

So, in this case,

`${pet}s`

is equivalent to

pet + 's'

You can even see how easy it is now to read this part of the code.

Answer 4

I assume you are new to JavaScript. If that is not the case then please forgive my previous statement.

In JavaScript, when you use a + between two string objects, the result is an appended string.

What it means is,

let appendedString = "string1" + "string2" ;
console.log(appendedString)
//output = string1string2

Now, for your example, you were supposed to append an 's' at the end of each string to transform that string into its plural form.

Thus the hint was to iterate over each string using a for loop and append an ''s" to each one of them.

Now, for iteration, my first approach would be to use the map function . But, to be precise it really doesn't matter in this particular exmaple. Hope, that makes it clear for you.

Answer 5

I loved this question. For this job you don't need any for loop in JS. The is Array.prototype.map() ; Let's also handle the irregularities.

 var pets = ['dog', 'cat', 'rat', 'deer', 'goose', 'mouse'], lut = {mouse: "mice", goose: "geese", deer: "deer"}, pluralPets = pets.map(p => lut[p] ? lut[p] : p+"s"); console.log(pluralPets); 

Answer 6

If you are using the for loop approach which I believe you are looking for, a better way to write Rayon's answer would be;

 var pets = ['cat', 'dog', 'rat']; var length = pets.length; for (i = 0; i < length; i++) { pets[i] = pets[i] + 's'; } console.log(pets);