How to improve app performance with StrictMode?

Do you want to optimize your app's performance and improve the user experience? One of the best ways to do so is by using StrictMode. This feature in React helps developers identify potential issues and fix them before they impact the user. In this blog, we'll dive deep into what StrictMode is and why it's crucial for app performance. We'll also explore how it works, how to implement it in your app, and the key differences between StrictMode and Use Strict. Don't let poor app performance affect your business or frustrate your users - read on to learn how StrictMode can help.

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Understanding StrictMode

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Defining StrictMode

StrictMode is a feature in React that helps identify potential problems in your code by enabling additional checks and warnings. It highlights common mistakes and ensures that your code follows best practices, leading to improved performance, better debugging, and overall cleaner code.

To enable StrictMode in JavaScript, we simply add 'use strict'; at the top of our files. This statement is not just a string, but a literal expression ignored by earlier versions of JavaScript. The statement tells the JavaScript engine to parse the code in a strict operating context. This strict context prevents certain actions from being taken and throws more exceptions (that's a good thing).

The beauty of StrictMode is that it helps us to write cleaner code, like preventing us from using a variable before declaring it. This is because variables in StrictMode are, by default, confined to the scope of the block statements they are defined within, unlike in normal JavaScript semantics where they can accidentally create global variables.

StrictMode makes it easier to write "secure" JavaScript by changing previously accepted "bad syntax" into real errors. For example, in normal code, mistyping a variable name creates a new global variable. In StrictMode, this will throw an error, making it impossible to accidentally create a global variable.

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     'use strict';
    let myVariable = 'Test';
    myVariabble = 'Test'; // This will throw an error in strict mode
     

In React, we have a similar concept called StrictMode. It is a wrapper component that checks the code inside it for potential problems. It does not render any visible UI, but activates additional checks and warnings for its descendants.

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     import React from 'react';
    
    function ExampleComponent() {
      return (
        <React.StrictMode>
          <div>
            {/* Your code here */}
          </div>
        </React.StrictMode>
      );
    }
    
    export default ExampleComponent;
     

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Importance of StrictMode for App Performance

StrictMode is a powerful tool for optimizing React applications. It helps to identify components with unsafe lifecycles, warns about legacy string ref API usage, and detects unexpected side effects.

By wrapping parts of our app with the <React.StrictMode> tag, we can enable checks and warnings for those parts only. This means we can gradually opt-in to StrictMode, without having to convert our entire script at once.

StrictMode function components render twice in order to detect any problems with the initial render and the subsequent updates. This double-rendering is only in development mode, and no extra renders occur in the production build.

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     import React from 'react';
    
    function App() {
      return (
        <React.StrictMode>
          <ComponentOne />
          <ComponentTwo />
        </React.StrictMode>
      );
    }
    
    export default App;
     

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How StrictMode Works?

StrictMode is a tool that helps us write better JavaScript code. It enforces stricter parsing and error handling on your JavaScript code at runtime. Code errors that would otherwise have been ignored or would have failed silently will now generate errors or throw exceptions, alerting you sooner to problems in your code and directing you to potential fixes.

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Identifying Unsafe Lifecycles

One of the key features of StrictMode in React is the ability to identify unsafe lifecycles in your components. Certain legacy lifecycle methods are considered unsafe for use in async rendering and are often a source of bugs. These include componentWillMount, componentWillReceiveProps, and componentWillUpdate.

When you wrap your components with <React.StrictMode>, it will warn you in the console if any of these unsafe lifecycle methods are used. This is extremely helpful in preparing your app for future versions of React, which may remove these lifecycle methods in favor of safer alternatives.

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     import React from 'react';
    
    class MyComponent extends React.Component {
      componentWillMount() {
        // This will generate a warning in strict mode
      }
    
      render() {
        return <div>Hello, world!</div>;
      }
    }
    
    function App() {
      return (
        <React.StrictMode>
          <MyComponent />
        </React.StrictMode>
      );
    }
    
    export default App;
     

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Warning About Legacy String Ref API Usage

Another feature of StrictMode is the warning about legacy string ref API usage. In the past, it was common to use the string ref API to reference an element in your render method. However, this approach has issues and is considered a legacy. String refs can create bugs, are less efficient, and are not recommended.

When you use StrictMode, it will warn you if you're using the legacy string ref API. This encourages you to switch to the newer callback ref API or the React.createRef() API, both of which are safer and more efficient.

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     import React from 'react';
    
    class MyComponent extends React.Component {
      render() {
        return <div ref="myDiv">Hello, world!</div>; // This will generate a warning in strict mode
      }
    }
    
    function App() {
      return (
        <React.StrictMode>
          <MyComponent />
        </React.StrictMode>
      );
    }
    
    export default App;
     

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What’s the difference between StrictMode and Use Strict?

While both StrictMode and 'use strict' are tools that help us write better and safer code, they serve different purposes and are used in different contexts.

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Key Features of StrictMode

StrictMode is a tool specific to React. It's a wrapper component that checks the code inside it for potential problems. It does not render any visible UI but activates additional checks and warnings for its descendants.

Some of the key features of StrictMode include:

• Identifying components with unsafe lifecycles.
• Warning about legacy string ref API usage.
• Detecting unexpected side effects.
• Detecting legacy context API.

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     import React from 'react';
    
    function App() {
      return (
        <React.StrictMode>
          <Component />
        </React.StrictMode>
      );
    }
    
    export default App;
     

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Key Features of Use Strict

On the other hand, 'use strict' is a directive in JavaScript that enables StrictMode. StrictMode applies to entire scripts or to individual functions. It helps catch common coding mistakes and "unsafe" actions such as:

• Using a variable without declaring it.
• Deleting variables, functions, or function arguments.
• Duplicating parameter names in function declarations.
• Writing to read-only or non-writable global variables.

To enable StrictMode in JavaScript, we add 'use strict'; at the top of our JavaScript files or functions.

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     'use strict';
    
    function myFunction() {
      // code
    }
     

In conclusion, while both StrictMode and 'use strict' help us write better code, they are used in different contexts. StrictMode is specific to React and helps catch potential problems in React components, while 'use strict' is a JavaScript directive that helps catch common coding mistakes and "unsafe" actions.

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How to Implement StrictMode in Your App?

Implementing StrictMode in your React application is a straightforward process. Here's a step-by-step guide to help you do it.

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Step-by-step Guide for Implementation

1. Identify where to apply StrictMode: You can apply StrictMode to your entire application, or to specific parts of it. It's often a good idea to start by applying it to smaller, isolated parts of your application, and then gradually expand its coverage as you resolve any warnings or errors that it uncovers.

2. Import StrictMode: To use StrictMode, you need to import it from React.

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     import React from 'react';
     

3. Wrap your components with StrictMode: Next, you need to wrap the components you want to check with the <React.StrictMode> tag. Any components or elements inside this tag will be checked by StrictMode.

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     import React from 'react';
    
    function App() {
      return (
        <React.StrictMode>
          <Component />
        </React.StrictMode>
      );
    }
    
    export default App;
     

4. Check the console for warnings or errors: Once you've wrapped your components with StrictMode, you should check your console for any warnings or errors. StrictMode will not cause your application to crash, but it will highlight potential issues in your console.

5. Resolve any issues: If StrictMode highlights any issues, you should resolve them. This might involve refactoring your code or changing your approach to certain problems.

6. Expand the coverage of StrictMode: Once you've resolved any issues in the parts of your application covered by StrictMode, you can expand its coverage to include more parts of your application.

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By following these steps, you can gradually improve the quality of your code and make your application more robust and maintainable.

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What are the potential issues when not using StrictMode?

Not using StrictMode in your React application or 'use strict' in your JavaScript code can lead to several potential issues:

1. Silent Errors: Without StrictMode, JavaScript fails silently without throwing any error, making it hard to debug and find the root cause of an issue. With StrictMode enabled, the JavaScript engine will throw errors for potentially problematic actions, making it easier to identify and fix issues.

2. Variable Leakage: In normal JavaScript, if you forget to use the 'let' keyword when declaring a new variable, you will accidentally create a global variable. This can lead to unexpected behavior in your code. StrictMode prevents this by throwing an error when it encounters a variable that has not been declared.

3. Unsafe Lifecycle Methods: In React, certain lifecycle methods are considered unsafe for use in async rendering and are often a source of bugs. StrictMode will warn you if any of these unsafe lifecycle methods are used in your components, helping you to avoid potential issues.

4. Legacy String Ref API Usage: The legacy string ref API in React has issues and is considered legacy. If you use StrictMode, it will warn you if you're using the legacy string ref API, encouraging you to switch to the newer callback ref API or the React.createRef() API, both of which are safer and more efficient.

5. Mutation of Read-Only Global Objects: Without StrictMode, you can accidentally mutate read-only global objects (like undefined). StrictMode prevents this by throwing an error when such an action is attempted.

6. Duplicate Parameter Values: Without StrictMode, you can create a function with duplicate parameter names. This can lead to confusion and unexpected behavior in your code. StrictMode prevents this by throwing an error when it encounters a function with duplicate parameter names.

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Make Use of StrictMode in Your React Applications!

StrictMode in JavaScript and StrictMode in React are indispensable tools for writing high-quality code. They help catch potential issues early, enforce better coding practices, and prepare your code for future versions of JavaScript and React.

By enabling StrictMode in JavaScript, you can prevent silent errors, avoid accidentally creating global variables, and enforce stricter parsing and error handling. This leads to cleaner, more readable code that is easier to debug and maintain.

With React's StrictMode, you can identify components with unsafe lifecycles, get warnings about legacy string ref API usage, and detect unexpected side effects. This helps you write safer React code and prepares your app for future versions of React.

Remember, the goal of these tools is not to make your life as a developer harder but to help you write better code. They might take some getting used to, but once you do, you'll find they're invaluable for improving the quality of your code and making your apps more robust and reliable. I highly recommend making use of StrictMode. They're tools that I wouldn't want to code without.