JavaScript beginner: 5 things to understand first

programming

"I've heard of JavaScript, but what can it do?" "I don't know where to start learning..."

For beginners who have such concerns.

JavaScript isThe magical technology that makes web pages move and respond to button clicksis.

In this article,Easy to understand even for beginners,
The first 5 basic grammar points to rememberDetailed explanation with concrete examplesI will.

This is the perfect content for you if you want to take the first step with confidence.

Learn how to write variables and constants

Conclusion: Save your data with let and const

In JavaScript, informationvariableorconstantSave it and reuse it.

Examples of variables (things that change):

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Examples of constants (things that don't change):

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Let allows reassignment,const is a fixed valueThere is a difference:

Common mistakes and solutions:

  • constIf you define it and then try to change the value later, an error occurs.
    → "If you think you might change it later, use let."

Let's try using conditional branching (if statements)

Conclusion: Use if to separate processing according to conditions

The if statement is used when you want something to happen only when a certain condition is met.

Example: Judging by test scores

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); } ); } ); }

Common mistakes:

  • =(assignment) and==or===confuse (compare)
    → ===determines whether the types and values are the same.

Understanding repetitive processing (for statement)

Conclusion: The for statement is useful when you want to perform the same process multiple times.

For example, to count from 1 to 5, you would write it like this:

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(

explanation:

  • i = 1 is the number of starts
  • i <= 5 is the end condition
  • i++ is an operation that increases by 1

Common mistakes:

  • i++ If you forget, it will become an infinite loop.
    → Be sure to ensure that the termination condition is met.

Define and reuse functions

Conclusion: Putting it all together in a function makes it easier to use

A function is a set of operations that can be named and called multiple times.

example:

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);

Common uses:

  • Display a message when the button is pressed
  • Calculate and display the numbers

Basics of event processing and HTML integration

Conclusion: Combined with HTML, it can react to user actions.

The real strength of JavaScript is its ability to work in conjunction with web pages.

Example: Display a message when a button is pressed

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Points to note:

  • onclick specifies the event within the HTML tag
  • alert() is a function that will be displayed as a popup on the screen

Common JavaScript errors and how to fix them

Conclusion: Spelling and grammar mistakes make up the majority

Common stumbling points:

  • Uncaught Reference Error: Use of undefined variable
  • SyntaxErrorForgotten closing parentheses or semicolons
  • TypeError: A function or value is used incorrectly

Solution:

  • Check the error statement in Google Chrome's developer tools
  • Use the completion feature of your code editor (such as VSCode)
  • Try something small and see the results as you go

Completed code: App that displays greetings when you enter a name

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< =>
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  < =>
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  < = = =>
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Summary: 5 grammar points to improve your English

Once you master the basics of JavaScript, the things you can do will expand dramatically.

  • Variables and ConstantsSave data with
  • If StatementBranch according to conditions
  • for statementRepeat with
  • functionSummarize the process with
  • eventRespond to user actions with

By combining these,Learn the basics of all web applications.

Even if you don't understand it at first, the quickest way to learn it is to write it out and try it out!

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