Svelte Tutorial - 9 - Conditional Rendering

Codevolution
16 May 202105:52

Summary

TLDRThis video tutorial explains how to conditionally render HTML elements in Svelte applications using 'if', 'else', and 'else if' blocks. It demonstrates with an example where a variable's value determines the displayed message, such as 'zero', 'positive', 'negative', or 'not a number'. The tutorial walks through the syntax and usage of these blocks, showing how to update the UI based on script-defined data, making it simple to handle multiple conditions with clear and practical examples.

Takeaways

  • 😀 Building web applications with Svelte involves using special HTML blocks to conditionally render elements based on certain conditions.
  • 🔑 Svelte provides three special blocks: `if`, `else`, and `elsif`, which function similarly to traditional programming language constructs.
  • 📝 The `if` block in Svelte uses a syntax of `{#if ...}` to evaluate an expression and render HTML if the expression is true.
  • 📚 The `else` block is used to render alternative content when the `if` block condition is false, utilizing `{:else ...}` syntax.
  • 🔄 The `elsif` block, represented by `{:else if ...}`, allows for additional conditions to be checked after the initial `if` block.
  • 🎯 An example given in the script involves checking a variable to determine if it's zero, positive, negative, or not a number, and rendering HTML accordingly.
  • 📌 The `#` symbol within curly braces denotes the start of an `if` block, while the `/` symbol signifies the end of the block.
  • 🔍 Conditional rendering in Svelte is demonstrated by changing the value of a variable and observing the changes in the browser output.
  • 📈 The script explains how to progressively build up conditional statements by adding `else if` blocks for multiple conditions.
  • 🛠️ The final example in the script shows how to handle various conditions by using a combination of `if`, `else`, and `elsif` blocks to render different HTML elements.
  • 📺 The video script concludes with a demonstration of the conditional rendering working as expected with different values assigned to the variable.

Q & A

  • What are the three special HTML blocks provided by Swelt for conditional rendering?

    -The three special HTML blocks provided by Swelt are the 'if' block, 'else' block, and 'elsif' block.

  • How do the conditional blocks in Swelt differ from traditional programming language constructs?

    -The conditional blocks in Swelt differ in that they are used to render HTML elements rather than execute logic.

  • What is the syntax for starting an 'if' block in Swelt?

    -The syntax for starting an 'if' block in Swelt is '{#if expression}'.

  • How do you close an 'if' block in Swelt?

    -An 'if' block in Swelt is closed with '}}' followed by the 'if' keyword.

  • What is the purpose of the 'else' block in Swelt's conditional rendering?

    -The 'else' block in Swelt is used to render HTML elements when the 'if' condition evaluates to false.

  • What symbol is used to represent the continuation of an 'else' block in Swelt?

    -The continuation of an 'else' block in Swelt is represented by a colon ':'.

  • How is the 'elsif' block used in Swelt to handle multiple conditions?

    -The 'elsif' block is used after the 'if' block to check for additional conditions, using the syntax '{:else if condition}'.

  • What happens when none of the conditions in the 'if', 'else if', and 'else' blocks are met?

    -When none of the conditions are met, no HTML elements are rendered, unless specified otherwise in the script.

  • Can you provide an example of how to check if a number is negative in Swelt?

    -To check if a number is negative in Swelt, you would use an 'else if' block with the condition '{:else if num < 0}'.

  • How can you display different messages based on whether a number is zero, positive, negative, or not a number in Swelt?

    -You can use a combination of 'if', 'else if', and 'else' blocks to check the conditions and render the appropriate message in Swelt.

  • What does the 'hash f' within curly braces represent in Swelt's conditional blocks?

    -The 'hash f' within curly braces in Swelt represents the opening of the conditional block where the expression is evaluated.

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SvelteConditional RenderingUI DevelopmentJavaScriptHTML ElementsProgramming LogicWeb DevelopmentFrontendTemplate SyntaxDynamic Content
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