Javascript tutorial Array編

JavaScript Arrayオブジェクトが持つmethod

下記のコードを実行すると、methodの一覧を確認することができます。

index.js

    console.log(Array.prototype);

この中から、いくつかピックアップして紹介します。

index.js

    const shopping = ["bread", "milk", "cheese", "hummus", "noodles"];
    
    // Accessing and modifying array items
    console.log(shopping[0]);
    // Modify an item in an array
    shopping[0] = "tahini";
    
    // Note that an array inside an array
    const random = ["tree", 759, [0, 1, 2]];
    console.log(random[2][2]);
    
    // Finding the index of items in array
    const birds = ["Parrot", "Falcom", "Owl"];
    console.log(birds.indexOf("Owl"));
    console.log(birds.indexOf("Rabbit"));
    
    // Adding items
    const cities = ["Manchester", "Liverpool"];
    cities.push("Cardiff");
    console.log(cities);
    cities.push("Bradford", "Brighton");
    console.log(cities);
    const newLength = cities.push("Bristol");
    console.log(newLength);
    
    // To add an item to the start of the array
    cities.unshift("Edinburgh");
    console.log(cities);
    
    // Removing items
    // To remove the last item from the array
    cities.pop();
    console.log(cities);
    
    // To remove the first item from an array
    cities.shift();
    console.log(cities);
    
    // To remove an item you know the index
    const index = cities.indexOf("Liverpool");
    if (index !== -1) {
      cities.splice(index, 2);
    }
    console.log(cities);
    
    // Accessing every item
    for (const city of cities) {
      console.log(city);
    }
    
    function double(number) {
      return number * 2;
    }
    const numbers = [5, 2, 7, 6];
    const doubled = numbers.map(double);
    console.log(doubled);
    
    // To create a new array containing only the items in the original array that match some test
    function isLong(citi) {
      return citi.length > 8;
    }
    const longer = cities.filter(isLong);
    console.log(longer);
    
    // Converting between strings and arrays
    const data = "Manchester,London,Liverpool,Birmingham,Leeds,Carlisle";
    
    // Split it at each comma
    const newCities = data.split(",");
    console.log("Length:" + newCities.length, newCities);
    
    // The opposite way
    const oppositeCityes = newCities.join(",");
    console.log(oppositeCityes);
    
    // Another way of converting an array to a string
    const dogNames = ["Rocket", "Flash", "Bella", "Slugger"];
    console.log(dogNames.toString());
    
    // A valid array index
    console.log(Object.keys(cities));    

参考資料