Mihai Serban

Cluj-Napoca, Romania 🇷🇴

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ES6 cheatsheet  —  Arrow Functions

Serban Mihai / 20 October 2018

~1 min read

ES6 Arrow functions

Arrows are a function shorthand using the => syntax. Arrow functions allow you to preserve the lexical value of this.

Take the example below where we have a nested function, in which we would like to preserve the context of this from its lexical scope:

function Person(name) {  
    this.name = name;  
}  

Person.prototype.prefixName = function (arr) {  
    return arr.map(function (character) {  
        return this.name + character; // Cannot read property 'name' of undefined  
    });  
};

Using Arrow Functions, the lexical value of this isn't shadowed and we can re-write the above as shown:

function Person(name) {  
    this.name = name;  
}  

Person.prototype.prefixName = function (arr) {  
    return arr.map(character => this.name + character);  
};

If an arrow is inside another function, it shares the arguments variable of its parent function. Example:

// Lexical arguments  
function square() {  
  let example = () => {  
    let numbers = [];  
    for (let number of arguments) {  
      numbers.push(number * number);  
    }  

    return numbers;  
  };  

  return example();  
}  

square(2, 4, 7.5, 8, 11.5, 21); // returns: [4, 16, 56.25, 64, 132.25, 441]

You can find a more complete ES6 cheetsheet on my Github page.

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