Learn more about JavaScript syntax errors and how to prevent them

Learn more about JavaScript syntax errors and how to prevent them

Learn more about JavaScript syntax errors and how to prevent them

• Learn more about JavaScript syntax errors and how to prevent them
• • 1. Why do you need to know about grammatical errors?
• 2. What are the common grammatical errors?
• • 2.1 Missing or unmatched quotes
• 2.2 Missing or mismatched brackets
• 2.3 The missing comma
• 2.4 Missing semicolon
• 2.5 Multilingual grammar confusion
• 3. How to prevent these errors?
• • 3.1 Code Editor
• 3.2 Static code analysis tools
• 3.3 TypeScript
• 3.4 First line indentation
• 4. Summary

Learn more about JavaScript syntax errors and how to prevent them

Syntax errors are a common problem programmers encounter. Missing parentheses or square brackets can prevent code from compiling or executing, causing lost work time and frustration. Other common mistakes include missing quotes or commas, or even using completely wrong syntax.

The best solution to this problem is to prevent syntax errors from occurring in the first place. If you stay alert to the most common mistakes, you can correct them before deployment. There are also various automated tools that can do this detection for you.

In this article, you will learn more about syntax errors in JavaScript. You'll see some examples of common syntax errors, as well as techniques and tools on how to fix them and keep them out of your code.

1. Why do you need to know about grammatical errors?

Syntax errors, also known as parsing errors, occur when developers incorrectly use predefined constructs or language patterns. Typos or other errors result in invalid code. These errors include open or mismatched parentheses, missing parentheses or punctuation, or misspelled keywords.

Here are some reasons why you need to be aware of syntax errors:

• The program will not compile or run successfully until all syntax errors are corrected. Avoiding this mistake can help you achieve more efficient and accurate coding.
• It's easy to reduce this error if you understand it. Browser Developer Tools displays JavaScript syntax errors in the console and pinpoints the line of code where the error occurred, letting you know where to start looking.
• Syntax errors often prevent build tools from running, meaning you can't build or deploy your application. If there is no build process and raw JavaScript is deployed, these errors will occur at runtime.

2. What are the common grammatical errors?

Here are some examples of syntax errors that often get developers into trouble.

2.1 Missing or unmatched quotes

Quotes often cause problems. Errors include adding an opening quote without closing it, or trying to close a double quote with a single quote (or vice versa). Adding more quotes will also cause a syntax error because the additional quotes will not match.

For example:

 
    // Missing quotation marks in the last item
    let arr = ["Joy", "Ruby", "Gail]   
    

2.2 Missing or mismatched brackets

Another common mistake is using an opening bracket without a matching closing bracket. Trying to wrap a left curly brace with a square bracket or vice versa can also cause this error.

For example:

 
    function check(x){
        if(x === 10){
          if(x === 10){ return true
        } else {
          return false
        // Missing right braces.
      }
    
    // or
    
    let arr = [
        {
            "name": "Lynn"
        }, { "name": "Lynn
        {
            "name": "Ruby"
        }, { "name": "Ruby
        {
            "name": "Phil"
        }
        } // Should be right square brackets
    

2.3 The missing comma

If you forget to add commas between items of an array or object, you'll get a syntax error:

 
    // Missing comma
    let arr ["apple", "orange" "pear"]   
    

2.4 Missing semicolon

Forgetting a semicolon where a semicolon is required, such as in fora loop, is another cause of JavaScript syntax errors:

 
    let arr = [0, 1, 2, 3]
    for(let i =0; i <= arr.length i++){   // A semicolon is missing after the second statement.
      console.log(arr[i] * 2)
    }
    

2.5 Multilingual grammar confusion

As you learn more programming languages, you may mistakenly try to use another language's syntax in JavaScript. You need to remember the rules of JavaScript and pay attention to them while coding.

The following example contains a whileloop that follows Python syntax, which causes an error when used in JavaScript:

 
    function check(x){
        while(x > 5):
         return x + 1
    }
    

3. How to prevent these errors?

There are tools and best practices you can use to avoid syntax errors in your code. Here are some examples.

3.1 Code Editor

These tools provide functionality to help you write and debug code. Its features include code auto-completion (which reduces the likelihood of you missing a closing bracket or parenthesis) and syntax highlighting (which uses specific colors to alert you to syntax errors in your code).

In the first image below, you'll see a syntax error highlighted in Visual Studio Code; in the second part, you'll see what the code editor looks like when the error is fixed:

While most code editors offer built-in features to aid debugging, some of these features work by default, while others may require you to change basic configuration or settings first.

3.2 Static code analysis tools

Static code analysis tools help detect errors and potential issues in continuous integration workflows before releasing code to production . These tools scan your code and compare it to predefined rules to find errors. ESLint and JSLint are examples of static code analysis tools.

ESLint allows you to apply rules that can be used to draw attention to specific patterns, but it may encounter some syntax errors. Depending on the rules you configure, function foo(){}}a malformed function declaration like this may make the code unparseable. ESLint will stop highlighting other issues because the code cannot be read or interpreted correctly.

3.3 TypeScript

TypeScript can help provide insight into syntax errors and how to resolve them. Instead of testing and encountering errors at runtime, you can use the TypeScript compiler to display errors in the terminal at compile time.

3.4 First line indentation

Indenting code is a standard practice that makes it easier to read code and find missing square brackets or parentheses. Tools like Prettier , ESLint, and Beautify can help you format your code properly, making it clearer and more consistent, thereby improving code quality.

4. Summary

Even the smallest mistakes can cause big problems in your code. As you learned in this article, you need to be able to detect syntax errors in your JavaScript applications so that detection and other tools that rely on parsing can provide feedback on your code so that you can deploy and publish it.

If you keep these tips and tools in mind as you write your code, you should be able to find and fix these problems. This will improve the quality of your software and speed up your workflow.