What are the methods of built-in objects in js?

Title: Common methods and code examples of JavaScript built-in objects

Abstract: JavaScript, as a powerful scripting language, often uses built-in objects in development. This article will introduce commonly used built-in objects and their methods in JavaScript, and provide corresponding code examples.

1. String object (String)

1. charAt()
   Description: Get the character at the specified position in the string according to the index.
   Sample code:

   let str = "Hello World!";
   console.log(str.charAt(0));  // 输出：H

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2. concat()
   Description: Used to concatenate two or more strings.
   Sample code:

   let str1 = "Hello";
   let str2 = "World";
   console.log(str1.concat(" ", str2));  // 输出：Hello World

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3. indexOf()
   Description: Returns the first matching index value of the specified substring in the string.
   Sample code:

   let str = "Hello World!";
   console.log(str.indexOf("o"));  // 输出：4

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2. Numeric object (Number)

1. toFixed()
   Description: Convert the number to A string specifying the number of decimal places.
   Sample code:

   let num = 3.1415926;
   console.log(num.toFixed(2));  // 输出：3.14

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2. toString()
   Description: Convert a number to a string.
   Sample code:

   let num = 123;
   console.log(num.toString());  // 输出："123"

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3. isNaN()
   Description: Determine whether a value is NaN (non-numeric value).
   Sample code:

   console.log(isNaN("Hello"));  // 输出：true
   console.log(isNaN(123));      // 输出：false

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3. Array object (Array)

1. push()
   Description: Add to the end of the array One or more elements and returns the length of the array after adding new elements.
   Sample code:

   let fruits = ["apple", "banana"];
   console.log(fruits.push("orange"));  // 输出：3
   console.log(fruits);  // 输出：["apple", "banana", "orange"]

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2. pop()
   Description: Remove the last element of the array and return the element.
   Sample code:

   let fruits = ["apple", "banana", "orange"];
   console.log(fruits.pop());  // 输出："orange"
   console.log(fruits);  // 输出：["apple", "banana"]

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3. join()
   Description: Concatenate array elements into strings, separated by the specified delimiter.
   Sample code:

   let fruits = ["apple", "banana", "orange"];
   console.log(fruits.join(", "));  // 输出："apple, banana, orange"

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The above are just some of the commonly used methods of JavaScript’s built-in objects. There are many other useful methods that are not listed one by one. In order to better use JavaScript built-in objects, it is recommended to view the relevant documentation and conduct more in-depth study and practice.

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