What is let-* in Angular 2 templates?

What is `let-*` in Angular 2 templates?

🤔 Have you ever come across the let-* syntax inside an Angular 2 template? 🤷‍♀️

You're not alone! Many developers have found this assignment syntax intriguing and have wondered what it does and how it works. Let's dive into the world of let-* and demystify its magic! ✨

Understanding the `let-*` syntax

When you encounter let-* in an Angular 2 template, it is used for template variables. These variables allow you to assign values to elements within the template, making it easy to access and manipulate them.

In the given example:

<template let-col let-car="rowData" pTemplate="body">
    <span [style.color]="car[col.field]">{{car[col.field]}}</span>
</template>

The let-col assigns the value of col to the current iteration item in the template. The let-car="rowData" assigns the value of rowData to the variable car. We can then use these variables (col and car) within the template to display data or perform any necessary logic.

The difference between `let-something` and `let-something="something else"`

The syntax let-something without an assigned value is used for iterating over an array or collection of items. It assigns each item to the variable, making it accessible within the template. This is similar to the traditional *ngFor directive in Angular.

On the other hand, the syntax let-something="something else" allows you to explicitly assign a value to the template variable. In the example provided, let-car="rowData" assigns the value of rowData to the variable car. This is useful when you want to give a specific name to a variable or assign a value that is not directly available in the iteration items.

Solving common issues

Issue #1: Accessing values in an ngFor loop

🚩 Problem: You're using an *ngFor loop in your template, and you want to access the current item within the loop for further processing or display. However, you're unsure how to do it.

💡 Solution: Use the let-* syntax to declare a template variable and assign the value of the iteration item to it. You can then reference this variable anywhere within the template.

Example:

<ul>
  <li *ngFor="let item of items; let index = index">
    <span>{{index}} - {{item}}</span>
  </li>
</ul>

In this example, let item of items iterates over the items array, and let index = index assigns the current index value to the index variable within the template.

Issue #2: Assigning custom names to variables

🚩 Problem: You have a specific name in mind for a template variable, but the items in your iteration do not have the same property or name.

💡 Solution: Use the let-something="something else" syntax to assign a custom value to the template variable.

Example:

<ul>
  <li *ngFor="let user of users; let userName = user.name">
    <span>{{userName}} - {{user.email}}</span>
  </li>
</ul>

In this example, we use let userName = user.name to assign the value of user.name to the userName template variable.

Conclusion

🎉 Congratulations! You've unlocked the secret of the let-* syntax in Angular 2 templates! 🎉

Now you can use this powerful feature to simplify your code and make it more expressive. Remember, let-* allows you to assign values to template variables, giving you greater control and flexibility in your Angular 2 applications.

So go ahead, give it a try, and let your creativity flow! 🚀

What's your experience with let-* in Angular 2 templates? Do you have any cool use cases or tips to share? Let us know in the comments below! Let's keep the conversation going! 💬

What is let-* in Angular 2 templates?