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山岸 英樹

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Javascript で配列内の要素のインデックスを検索する

このチュートリアルでは、JavaScriptの配列 indexOf() と lastIndexOf() メソッドを使用して、配列内の要素の位置またはインデックスを見つける方法を学習します。

JavaScript配列 indexOf()

この indexOf() メソッドは、配列の最初の出現位置を見つけるために使用され、要素の最初の出現のインデックスを返します。要素が見つからない場合は、-1が返されます。

の構文 indexOf()

Array.indexOf(search, startIndex)

ここで、  メソッドは2つのパラメーターを受け入れます。indexOf()

  1. search引数は、配列内で検索したいということな要素です。
  2. startIndex これで、配列インデックスである関数は、検索を開始します。

注:- startIndex パラメーター値は、正または負の整数にすることができます。

JavaScript配列の例 indexOf() 

indexOf()メソッドの例を見てください。

という名前の数値配列があるとし arrます。以下を参照してください。

var arr = [10, 20, 30, 40, 50, 70, 10];

 

次の例では、このindexOf() メソッドを使用 してarr 配列内の要素を検索します 。

var arr = [10, 20, 30, 40, 50, 70, 10, 50];
console.log(arr.indexOf(10)); // 0
console.log(arr.indexOf(50)); // 4
console.log(arr.indexOf(70)); // 5
console.log(arr.indexOf(30)); // 2

次のオブジェクトの配列がある 場合、各オブジェクトには異なるプロパティがあります。以下を参照してください。

var obj = [
    {name: 'John Doe', age: 30},
    {name: 'Tom Bush', age: 20},
    {name: 'Bill Gate', age: 25}
];

次のステートメントは-1 、obj 配列の 最初の要素 とが  プロパティのsearchElement 値が同じで あっても 戻り ます。これは、それらが2つの異なるオブジェクトであるためです。nameages

console.log(obj.indexOf({
    name: 'John Doe',
    age: 30
})); // -1

JavaScript配列 lastIndexOf()

これはindexOf()メソッドに似ていますが、これらに1つの違いがあります。Javascript lastIndexOf()メソッドは、配列の最後の出現位置を見つけるために使用されます。要素が見つからない場合は-1を返します。

lastIndexOf() メソッドの構文 :

Array.lastIndexOf(searchElement[, fromIndex = Array.length - 1])

注:-indexOf() 方法や方法とは 基本的に異なり lastIndexOf() ます。1つはバックワード検索方法で、もう1つはフォワード検索方法です。

次の例を参照してください。


var arr = [10, 20, 30, 40, 50, 70, 10, 40];
console.log(arr.lastIndexOf(10));// 6
console.log(arr.lastIndexOf(40));// 7

配列内の要素を検索し、それが使用できない場合は、-1を返します。以下を参照してください。


var arr = [10, 20, 30, 40, 50, 70, 10, 40];
console.log(arr.lastIndexOf(100));// -1

結論

このチュートリアルでは、JavaScript配列indexOf() と lastIndexOf() メソッドを使用して配列内の要素を検索する方法を学習し ました。

#javascript 

リンク: https://www.tutsmake.com/javascript-array-indexof-lastindexof/

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 Javascript で配列内の要素のインデックスを検索する

Rahul Jangid

1622207074

What is JavaScript - Stackfindover - Blog

Who invented JavaScript, how it works, as we have given information about Programming language in our previous article ( What is PHP ), but today we will talk about what is JavaScript, why JavaScript is used The Answers to all such questions and much other information about JavaScript, you are going to get here today. Hope this information will work for you.

Who invented JavaScript?

JavaScript language was invented by Brendan Eich in 1995. JavaScript is inspired by Java Programming Language. The first name of JavaScript was Mocha which was named by Marc Andreessen, Marc Andreessen is the founder of Netscape and in the same year Mocha was renamed LiveScript, and later in December 1995, it was renamed JavaScript which is still in trend.

What is JavaScript?

JavaScript is a client-side scripting language used with HTML (Hypertext Markup Language). JavaScript is an Interpreted / Oriented language called JS in programming language JavaScript code can be run on any normal web browser. To run the code of JavaScript, we have to enable JavaScript of Web Browser. But some web browsers already have JavaScript enabled.

Today almost all websites are using it as web technology, mind is that there is maximum scope in JavaScript in the coming time, so if you want to become a programmer, then you can be very beneficial to learn JavaScript.

JavaScript Hello World Program

In JavaScript, ‘document.write‘ is used to represent a string on a browser.

<script type="text/javascript">
	document.write("Hello World!");
</script>

How to comment JavaScript code?

  • For single line comment in JavaScript we have to use // (double slashes)
  • For multiple line comments we have to use / * – – * /
<script type="text/javascript">

//single line comment

/* document.write("Hello"); */

</script>

Advantages and Disadvantages of JavaScript

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It is said that a digital resource a business has must be interactive in nature, so the website or the business app should be interactive. How do you make the app interactive? With the use of JavaScript.

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#hire dedicated javascript developers #hire javascript developers #top javascript developers for hire #hire javascript developer #hire a freelancer for javascript developer #hire the best javascript developers

Niraj Kafle

1589255577

The essential JavaScript concepts that you should understand

As a JavaScript developer of any level, you need to understand its foundational concepts and some of the new ideas that help us developing code. In this article, we are going to review 16 basic concepts. So without further ado, let’s get to it.

#javascript-interview #javascript-development #javascript-fundamental #javascript #javascript-tips

Ajay Kapoor

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Santosh J

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JavaScript compound assignment operators

JavaScript is unarguablly one of the most common things you’ll learn when you start programming for the web. Here’s a small post on JavaScript compound assignment operators and how we use them.

The compound assignment operators consist of a binary operator and the simple assignment operator.

The binary operators, work with two operands. For example a+b where + is the operator and the a, b are operands. Simple assignment operator is used to assign values to a variable(s).

It’s quite common to modify values stored in variables. To make this process a little quicker, we use compound assignment operators.

They are:

  • +=
  • -+
  • *=
  • /=

You can also check my video tutorial compound assignment operators.

Let’s consider an example. Suppose price = 5 and we want to add ten more to it.

var price = 5;
price = price + 10;

We added ten to price. Look at the repetitive price variable. We could easily use a compound += to reduce this. We do this instead.

price += 5;

Awesome. Isn’t it? What’s the value of price now? Practice and comment below. If you don’t know how to practice check these lessons.

Lets bring down the price by 5 again and display it.
We use console.log command to display what is stored in the variable. It is very help for debugging.
Debugging let’s you find errors or bugs in your code. More on this later.

price -= 5;
console.log(price);

Lets multiply price and show it.

price *=5;
console.log(price);

and finally we will divide it.

price /=5;
console.log(price);

If you have any doubts, comment below.

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