Syntax, Parameter and Return Value
Syntax:
_.once(func)
Parameters:
func (Function): The function to restrict to a single call.
Return Value:
(Function) - Returns the new restricted function.
Examples
Single Initialization Function:
JavaScript
var _ = require('lodash');
function initialize() {
console.log('Initialization completed');
}
var initializeOnce = _.once(initialize);
initializeOnce(); // Output: 'Initialization completed'
initializeOnce(); // No output on subsequent calls
You can also try this code with Online Javascript Compiler
Demonstrates ensuring an initialization function is only executed once.
One-Time Event Handler:
JavaScript
var button = document.getElementById('myButton');
var handleClickOnce = _.once(() => console.log('Button clicked'));
button.addEventListener('click', handleClickOnce);
You can also try this code with Online Javascript Compiler
// 'Button clicked' is logged only on the first click
Shows using _.once() for an event handler to respond to the first event only.
Single Execution in Asynchronous Operations:
JavaScript
function fetchData(callback) {
// Simulate fetching data
setTimeout(callback, 1000);
}
var logDataOnce = _.once(() => console.log('Data fetched'));
fetchData(logDataOnce);
fetchData(logDataOnce);
You can also try this code with Online Javascript Compiler
// 'Data fetched' is logged only once, even though fetchData is called twice
An example of using _.once() in asynchronous operations to avoid duplicate actions.
Preventing Duplicate Submissions:
JavaScript
function submitForm() {
console.log('Form submitted');
}
var submitFormOnce = _.once(submitForm);
submitFormOnce();
submitFormOnce(); // Subsequent calls do nothing
You can also try this code with Online Javascript Compiler
Output:
'Form submitted'
Demonstrates using _.once() to prevent duplicate form submissions.
Frequently Asked Questions
Can _.once() be reset to allow the function to run again?
No, once _.once() is applied to a function, it cannot be reset. The function will always return the result of the first call.
Does _.once() affect the original function?
No, _.once() does not alter the original function. It creates a new function with the once-only restriction.
Is _.once() suitable for functions with side effects?
Yes, _.once() is particularly suitable for functions with side effects that should only occur once, like initialization routines or API calls.
Conclusion
Lodash's _.once() method is a simple yet powerful tool for ensuring that a function is executed only a single time. It's especially useful for managing one-time operations, initialization tasks, and preventing duplicate actions in event-driven programming.
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