“Was sind Schließungen in JavaScript?” Code-Antworten

JavaScript -Schließung

function makeAdder(x) {
  return function(y) {
    return x + y;
  };
}

var add5 = makeAdder(5);
var add10 = makeAdder(10);

console.log(add5(2));  // 7
console.log(add10(2)); // 12

//my words: what this code do is basically a nested function that will return
//its inner function (un-activated). So var add5 in line 7 activated the outer
//function with 5 as parameter which makes add5 is now the nameless function at
//line 2 that will return 5 + y;

//MDN words:
//add5 and add10 are both closures. They share the same function body
//definition, but store different lexical environments. In add5's lexical
//environment, x is 5, while in the lexical environment for add10, x is 10.
Graceful Grivet

ES6 -Schließungen

var makeCounter = function() {
  var privateCounter = 0;
  function changeBy(val) {
    privateCounter += val;
  }
  return {
    increment: function() {
      changeBy(1);
    },
    decrement: function() {
      changeBy(-1);
    },
    value: function() {
      return privateCounter;
    }
  }
};

var counter1 = makeCounter();
var counter2 = makeCounter();
alert(counter1.value()); /* Alerts 0 */
counter1.increment();
counter1.increment();
alert(counter1.value()); /* Alerts 2 */
counter1.decrement();
alert(counter1.value()); /* Alerts 1 */
alert(counter2.value()); /* Alerts 0 */
Kaotik

Schließung in JavaScript

var counter = (function() {
  var privateCounter = 0;
  function changeBy(val) {
    privateCounter += val;
  }
  return {
    increment: function() {
      changeBy(1);
    },
    decrement: function() {
      changeBy(-1);
    },
    value: function() {
      return privateCounter;
    }
  };
})();

console.log(counter.value()); // logs 0
counter.increment();
counter.increment();
console.log(counter.value()); // logs 2
counter.decrement();
console.log(counter.value()); // logs 1
Gentle Grouse

Eine Schließfunktion

var returns_a_func = function () {
  var word = 'I can see inside '     function sentence(){    var word2 = 'I can also see outside. '     console.log(word + 'and ' + word2)   }   return sentence;
}var finalSentence = returns_a_func()finalSentence()
Glorious Gentoo

Was sind Schließungen in JavaScript?

/*A closure is the combination of a function bundled together (enclosed) with references
to its surrounding state (the lexical environment). In other words, a closure gives you 
access to an outer function’s scope from an inner function. In JavaScript, closures are 
created every time a function is created, at function creation time.*/

function init() {
  var name = 'Mozilla'; // name is a local variable created by init
  function displayName() { // displayName() is the inner function, a closure
    alert(name); // use variable declared in the parent function
  }
  displayName();
}
init();
Noble@247

Abschlussbeispiel

const add = (function () {
  let counter = 0;
  return function () {counter += 1; return counter}
})();

add();
add();
add();

// the counter is now 3
Muthukumar

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