Let us see how to execute a specified function only once in the life time of the program.
The Simple Way
The easiest way is to use a global variable and remember the function execution. We can then ignore all future invocations.
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let saidHello = false;
function sayHello() {
console.log("hello world");
saidHello = true;
}
function helloOnce() {
if (!saidHello) sayHello();
}
helloOnce(); // hello world
helloOnce(); // nothing
helloOnce();
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The Reusable Way
We can apply concepts similar to our debounce utility to execute a function once and only one time.
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function execOnce(fn, context) {
var result;
return function () {
if (fn) {
result = fn.apply(context || this, arguments);
fn = null;
}
return result;
};
}
function sayHello() {
console.log("hello world");
}
var helloOnce = execOnce(sayHello);
helloOnce(); // hello world
helloOnce(); // nothing but emptiness
helloOnce();
helloOnce();
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We have made the function reusable for any number of functions, and achieved the same goal as option (1).
