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onetime 
Ensure a function is only called once
When called multiple times it will return the return value from the first call.
Unlike the module once, this one isn't naughty and extending Function.prototype.
Install
$ npm install onetime
Usage
const onetime = require('onetime');
let i = 0;
const foo = onetime(() => ++i);
foo(); //=> 1
foo(); //=> 1
foo(); //=> 1
onetime.callCount(foo); //=> 3
const onetime = require('onetime');
const foo = onetime(() => {}, {throw: true});
foo();
foo();
//=> Error: Function `foo` can only be called once
API
onetime(fn, options?)
Returns a function that only calls fn once.
fn
Type: Function
Function that should only be called once.
options
Type: object
throw
Type: boolean
Default: false
Throw an error when called more than once.
onetime.callCount(fn)
Returns a number representing how many times fn has been called.
Note: It throws an error if you pass in a function that is not wrapped by onetime.
const onetime = require('onetime');
const foo = onetime(() => {});
foo();
foo();
foo();
console.log(onetime.callCount(foo));
//=> 3
fn
Type: Function
Function to get call count from.
onetime for enterprise
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