Tutorials

Lodash _.templateSettings.evaluate Property

Posted in lodash Tutorial

Updated on Oct 30, 2024

By Mari Selvan

👁️ 52 - Views

⏳ 4 mins

💬 1 Comment

Lodash _.templateSettings.evaluate Property

Photo Credit to CodeToFun

🙋 Introduction

In JavaScript development, templates are indispensable for generating dynamic content. Lodash provides a powerful templating feature through the _.template() function. Within this function, developers can leverage various properties of _.templateSettings to customize template behavior.

One such property is evaluate, which allows for the definition of custom delimiters for evaluation expressions within templates.

🧠 Understanding _.templateSettings.evaluate

The evaluate property within _.templateSettings is used to specify the delimiters for evaluation expressions in templates. These expressions are JavaScript code snippets that are evaluated, but their results are not directly inserted into the output string. Instead, they are used for control flow and logic within the template.

💡 Syntax

The syntax for the _.templateSettings.evaluate property is straightforward:

syntax.js

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_.templateSettings.evaluate = /<%([\s\S]+?)%>/g;

This sets the evaluation expression delimiter to <% ... %>, allowing JavaScript code to be executed within the template.

📝 Example

Let's dive into a simple example to illustrate the usage of the _.templateSettings.evaluate property:

example.js

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// Set custom evaluate delimiter
_.templateSettings.evaluate = /<%([\s\S]+?)%>/g;

// Define template string
const templateString = '<% if (loggedIn) { %> Welcome, <%= username %>! <% } else { %> Please log in. <% } %>';

// Compile template
const compiledTemplate = _.template(templateString);

// Render template with data
const renderedTemplate = compiledTemplate({ loggedIn: true, username: 'John' });

console.log(renderedTemplate);
// Output: "Welcome, John!"

In this example, the <% ... %> delimiters define JavaScript evaluation expressions within the template. Depending on the value of the loggedIn property, different content is rendered.

🏆 Best Practices

When working with the _.templateSettings.evaluate property, consider the following best practices:

Consistency in Delimiters:

Maintain consistency in delimiters throughout your templates to ensure readability and maintainability of code. Choose delimiters that align with your project's conventions and stick to them across all templates.
example.js
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```
_.templateSettings.evaluate = /<%([\s\S]+?)%>/g;
_.templateSettings.interpolate = /<%=([\s\S]+?)%>/g;
_.templateSettings.escape = /<%-([\s\S]+?)%>/g;
```
Escaping Delimiters:

Be mindful of escaping delimiters within your templates to prevent unintended parsing. Use appropriate escaping mechanisms or consider alternative delimiters if conflicts arise.
example.js
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```
_.templateSettings.evaluate = /<%([\s\S]+?)%>/g;
_.templateSettings.interpolate = /{{([\s\S]+?)}}/g;
```
Performance Considerations:

Evaluate the performance impact of custom delimiters, especially in scenarios involving complex templates or frequent template rendering. Optimize templates and minimize unnecessary evaluation for improved performance.
example.js
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```
_.templateSettings.evaluate = /<%([\s\S]+?)%>/g;

console.time('templateRendering');
const renderedTemplate = compiledTemplate(data);
console.timeEnd('templateRendering');
```

📚 Use Cases

Conditional Rendering:

The evaluate property enables conditional rendering within templates, allowing developers to control the output based on runtime conditions.
example.js
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```
_.templateSettings.evaluate = /<%([\s\S]+?)%>/g;

const templateString = '<% if (isAdmin) { %> Welcome, admin! <% } else { %> Access denied. <% } %>';
```
Iterative Rendering:

Iterative rendering, such as looping through arrays or objects, can be achieved using the evaluate property to define iteration logic within templates.
example.js
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```
_.templateSettings.evaluate = /<%([\s\S]+?)%>/g;

const templateString = '<% users.forEach(user => { %> <li><%= user.name %></li> <% }) %>';
```
Dynamic Layouts:

Dynamic layouts, where the structure of the template varies based on runtime conditions, can be implemented using the evaluate property to switch between different layout components.
example.js
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```
_.templateSettings.evaluate = /<%([\s\S]+?)%>/g;

const templateString = '<% if (isMobile) { %> Mobile layout: <%= content %> <% } else { %> Desktop layout: <%= content %> <% } %>';
```

🎉 Conclusion

The _.templateSettings.evaluate property in Lodash offers a flexible mechanism for defining custom delimiters for evaluation expressions within templates. By leveraging this property, developers can enhance the expressiveness and versatility of their templating solutions, enabling dynamic content generation in JavaScript applications.

By adhering to best practices and exploring diverse use cases, you can harness the full potential of the _.templateSettings.evaluate property in your Lodash projects.