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I just look at the once API of source in underscore.js, then wandering what is it the used for in the method, it seems doing nothing:
func = null
the source:
_.once = function(func) {
var ran = false, memo;
return function() {
if (ran) return memo;
ran = true;
memo = func.apply(this, arguments);
func = null;
return memo;
};
};
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What is an Underscore? Alternatively referred to as a low line, low dash, and understrike, the underscore ( _ ) is a symbol found on the same keyboard key as the hyphen. The picture shows an example of an underscore at the beginning and end of the word "Underscore."
- Quora Why is an underscore used in C? It is just like other characters but can be used for following purposes:- 1.Let’s name some identifiers… In the above written identifiers which one you find more readable RHS or LHS ?
A "blank" underscore is often used to indicate that a word or words is missing and n... (more)Loading…. An underscore is simply a line under a word or words, used as emphasis. Also called an underline. On an English-language keyboard, it can be inserted by highlighting a word and pressing CTRL + u.
What is the use of underscore keyword in Java 9? In earlier versions of Java, the underscore (" _ ") has used as an identifier or to create a variable name. Since Java 9, the underscore character is a reserved keyword and can't be used as an identifier or variable name.
What the function does can be found in the documentation:
Creates a version of the function that can only be called one time. Repeated calls to the modified function will have no effect, returning the value from the original call. Useful for initialization functions, instead of having to set a boolean flag and then check it later.
Why set func = null is explained in this commit message:
Assuming we'll never run the wrapped function again on _.once(), we can assign null to the
funcvariable, so function (and all its inherited scopes) may be collected by GC if needed.
78
From the official underscorejs website:
once _.once(function)
Creates a version of the function that can only be called one time. Repeated calls to the modified function will have no effect, returning the value from the original call. Useful for initialization functions, instead of having to set a boolean flag and then check it later.
var initialize = _.once(createApplication);
initialize();
initialize();
// Application is only created once.
http://underscorejs.org/#once
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