HTML과 DOM elements

<!DOCTYPE html>
<html>
<head>
<title>JavaScript Elements</title>
</head>
<body>
<div>
    <ul id='hello-list'>
        <li>list1</li>
        <li>list2</li>
        <li>list3</li>
    </ul>
</div>
 
<script type="text/javascript">
 
    var list4 = document.createElement("li");
    var node = document.createTextNode("Hello World");
    list4.appendChild(node);
 
    var element = document.getElementById("hello-list");
    element.appendChild(list4);hello-list
 
</script>
 
</body>
</html>

새 HTML 엘리먼트를 추가하려면 createElement()나 createTextNode() 메서드를 이용해 HTML 엘리먼트를 생성한 다음 그것을 기존 엘리먼트에 덧붙이면 된다.

클래스 이름 가져오기

<!doctype html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>
<body>
    <div id="parent-id">
        <p>hello word1</p>
        <p class="test">hello word2</p>
        <p >hello word3</p>
        <p>hello word4</p>
    </div>
    <script>
        var parentDOM = document.getElementById("parent-id");
        
        var test=parentDOM.getElementsByClassName("test");//test is not target element
        console.log(test);//HTMLCollection[1]

        var testTarget=parentDOM.getElementsByClassName("test")[0];//hear , this element is target
        console.log(testTarget);//<p class="test">hello word2</p>
    </script>
</body>
</html>

jQuery에서 특정 돔요소 삭제

<html>
<head>
  <style>
    p {
      background: yellow;
      margin: 6px 0;
    }
  </style>
  <script src="http://code.jquery.com/jquery-latest.js"></script>
</head>

<body>
  <p>Hello</p> how are
  <p>you?</p> 
  <button>Call remove() on paragraphs</button>
  <script>
    $("button").click(function() {
      $("p").remove();
    });
  </script>
</body>
</html>

$("element").remove()를 사용해 삭제할 수 있다.  hello를 포함한 모든 문단 제거 시  $("p").remove(":contains('Hello')"); 를 사용한다.

요소에 onclick 쓰기

<!DOCTYPE html>
<html>
<body>

<h1 onclick="changeText(this)">Click on this text!</h1>

<script>
function changeText(id) {
    id.innerHTML = "Ooops!";
}
</script>

</body>
</html>

 

클래스 요소를 삭제하기 

elements가 0 보다 큰 동안 parentNode.removeChild()를 이용해 삭제한다.

<!DOCTYPE html>
<html>
<body>

<button id="myBtn" onclick="displayDate()">Try it</button>
<div class="test">TEST</div>

<p id="demo"></p>

<script>
// if you use jQuery, $('.test').remove();
function removeElementsByClass(className){
    var elements = document.getElementsByClassName(className);
    while(elements.length > 0){
        elements[0].parentNode.removeChild(elements[0]);
    }
}
function displayDate() {
    document.getElementById("demo").innerHTML = Date();
    removeElementsByClass("test");
}
</script>

</body>
</html> 

 

Finding a String in a String

var str = "Please locate where 'locate' occurs!";
var pos = str.indexOf("locate");
var str = "Please locate where 'locate' occurs!";
var pos = str.indexOf("locate");

해당 인자의 인덱스를 반환한다.

var pos = str.indexOf("locate",15);

searches a string for a specified value and returns the position of the match

var str = "Please locate where 'locate' occurs!";
var pos = str.search("locate");  // 7

Extracting String Parts

slice() 메서드는 특정 문자열의 특정 부분을 잘라낼 수 있다. 

var str = "Apple, Banana, Kiwi";
var res = str.slice(7,13); // Banana

파라메터가 음수면 문자열 반대방향으로 부터 계산되어 잘라낸다.

var str = "Apple, Banana, Kiwi";
var res = str.slice(-12, -6); // Banana
var str = "Apple, Banana, Kiwi";
var res = str.slice(7); // Banana, Kiwi

The substring() Method

var str = "Apple, Banana, Kiwi";
var res = str.substring(7, 13); // Banana

The substr() Method

var str = "Apple, Banana, Kiwi";
var res = str.substr(7, 6); // Banana

Replacing String Content

replace() 메서드는 문자열을 찾아서 대체할 수 있다.

str = "Please visit Microsoft!";
var n = str.replace("Microsoft", "W3Schools");

모든 문자열의 대체가 필요하다면 정규식 표현법에 의해 /g 옵션을 사용한다.

str = "Please visit Microsoft and Microsoft!";
var n = str.replace(/Microsoft/g, "W3Schools");

 

concat() joins two or more strings:

var text1 = "Hello";
var text2 = "World";
var text3 = text1.concat(" ", text2); // Hello World!

 

Extracting String Characters

charAt() method returns the character at a specified index (position)

var str = "HELLO WORLD";
str.charAt(0);            // returns H

charCodeAt() method returns the unicode of the character at a specified index in a string

var str = "HELLO WORLD";

str.charCodeAt(0);         // returns 72

A string can be converted to an array with the split()

    var str = "a,b,c,d,e,f";
    var arr = str.split(",");
    document.getElementById("demo").innerHTML = arr[0];  / a
var txt = "Hello";       // String
txt.split("");           // Split in characters

 

Array

var cars = ["Saab", "Volvo", "BMW"];
var cars = new Array("Saab", "Volvo", "BMW");

Array:

var person = ["John", "Doe", 46];

Object:

var person = {firstName:"John", lastName:"Doe", age:46};
document.getElementById("demo").innerHTML = person.lastName;

Adding Array Elements

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.push("Lemon");                // adds a new element (Lemon) to fruits
var person = [];
person[0] = "John";
person[1] = "Doe";
person[2] = 46;
var x = person.length;         // person.length will return 3
var y = person[0];             // person[0] will return "John"
var person = [];
person["firstName"] = "John";
person["lastName"] = "Doe";
person["age"] = 46;
var x = person.length;         // person.length will return 0
var y = person[0];             // person[0] will return undefined

Converting Arrays to Strings

toString()

var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.toString(); // Banana,Orange,Apple,Mango

join()

var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.join(" * "); // Banana * Orange * Apple * Mango

pop() method removes the last element from an array

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.pop();              // Removes the last element ("Mango") from fruits
var fruits = ["Banana", "Orange", "Apple", "Mango"];
var x = fruits.pop();      // the value of x is "Mango"

push() method adds a new element to an array (at the end)

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.push("Kiwi");       //  Adds a new element ("Kiwi") to fruits
var fruits = ["Banana", "Orange", "Apple", "Mango"];
var x = fruits.push("Kiwi");   //  the value of x is 5

shift() method removes the first array element and "shifts" all other elements to a lower index

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.shift();            // Removes the first element "Banana" from fruits

unshift() method adds a new element to an array (at the beginning)

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon");    // Adds a new element "Lemon" to fruits

append a new element to an array

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits[fruits.length] = "Kiwi";          // Appends "Kiwi" to fruit

elements can be deleted by using the JavaScript operator delete

var fruits = ["Banana", "Orange", "Apple", "Mango"];
delete fruits[0];           // Changes the first element in fruits to undefined

sort() method sorts an array alphabetically

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.sort();            // Sorts the elements of fruits

reverse() method reverses the elements in an array

Numeric Sort

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a - b});  // 1,5,10,25,40,100

Use the same trick to sort an array descending

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return b - a}); //100,40,25,10,5,1

Sorting an Array in Random Order

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return 0.5 - Math.random()});

Find the Highest (or Lowest) Array Value

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a - b});
// now points[0] contains the lowest value
// and points[points.length-1] contains the highest value

 

Sorting Object Arrays

var cars = [
{type:"Volvo", year:2016},
{type:"Saab", year:2001},
{type:"BMW", year:2010}];
cars.sort(function(a, b){return a.year - b.year});

 

Input Validation Example

<!DOCTYPE html>
<html>
<body>

<p>Please input a number between 5 and 10:</p>

<input id="demo" type="text">
<button type="button" onclick="myFunction()">Test Input</button>
<p id="message"></p>

<script>
function myFunction() {
    var message, x;
    message = document.getElementById("message");
    message.innerHTML = "";
    x = document.getElementById("demo").value;
    try { 
        if(x == "") throw "empty";
        if(isNaN(x)) throw "not a number";
        x = Number(x);
        if(x < 5) throw "too low";
        if(x > 10) throw "too high";
    }
    catch(err) {
        message.innerHTML = "Input is " + err;
    }
}
</script>

</body>
</html>

 

Converting a JSON Text to a JavaScript Object

<html>
<body>

<h2>Create Object from JSON String</h2>

<p id="demo"></p>

<script>
var text = '{"employees":[' +
'{"firstName":"John","lastName":"Doe" },' +
'{"firstName":"Anna","lastName":"Smith" },' +
'{"firstName":"Peter","lastName":"Jones" }]}';

obj = JSON.parse(text);
document.getElementById("demo").innerHTML =
obj.employees[1].firstName + " " + obj.employees[1].lastName;
</script>

</body>
</html>

Storing Data

//Storing data:
myObj = { "name":"John", "age":31, "city":"New York" };
myJSON = JSON.stringify(myObj);
localStorage.setItem("testJSON", myJSON);

//Retrieving data:
text = localStorage.getItem("testJSON");
obj = JSON.parse(text);
document.getElementById("demo").innerHTML = obj.name;

How to loop through all properties in a JSON object

var myObj = { "name":"John", "age":30, "car":null };
for (x in myObj) {
    document.getElementById("demo").innerHTML += x + "<br>";
}

Result:
name
age
car
document.getElementById("demo").innerHTML += myObj[x] + "<br>";

John
30
null

Nested JSON Objects

myObj = {
    "name":"John",
    "age":30,
    "cars": {
        "car1":"Ford",
        "car2":"BMW",
        "car3":"Fiat"
    }
 }

You can access nested JSON objects by using the dot notation or bracket notation

x = myObj.cars.car2;
//or:
x = myObj.cars["car2"];

to modify any value

myObj.cars.car2 = "Mercedes";

to delete properties from a JSON object

delete myObj.cars.car2;

Arrays in JSON Objects

{
"name":"John",
"age":30,
"cars":[ "Ford", "BMW", "Fiat" ]
}
x = myObj.cars[0];  // using index  x -> Ford

You can access array values by using a for-in loop

for (i in myObj.cars) {
    x += myObj.cars[i];
}

Result:

Ford
BMW
Fiat

Or you can use a for loop:

for (i = 0; i < myObj.cars.length; i++) {
    x += myObj.cars[i];
}

 

Nested Arrays in JSON Objects

myObj = {
    "name":"John",
    "age":30,
    "cars": [
        { "name":"Ford", "models":[ "Fiesta", "Focus", "Mustang" ] },
        { "name":"BMW", "models":[ "320", "X3", "X5" ] },
        { "name":"Fiat", "models":[ "500", "Panda" ] }
    ]
 }

To access arrays inside arrays, use a for-in loop for each array

<html>
<body>

<p>Looping through arrays inside arrays.</p>

<p id="demo"></p>

<script>

var myObj, i, j, x = "";
myObj = {
    "name":"John",
    "age":30,
    "cars": [
        { "name":"Ford", "models":[ "Fiesta", "Focus", "Mustang" ] },
        { "name":"BMW", "models":[ "320", "X3", "X5" ] },
        { "name":"Fiat", "models":[ "500", "Panda" ] }
    ]
}

for (i in myObj.cars) {
    x += "<h2>" + myObj.cars[i].name + "</h2>";
    for (j in myObj.cars[i].models) {
        x += myObj.cars[i].models[j] + "<br>";
    }
}

document.getElementById("demo").innerHTML = x;

</script>

</body>
</html>

 

JSON From the Server

You can request JSON from the server by using an AJAX request

As long as the response from the server is written in JSON format, you can parse the string into a JavaScript object.

Use the XMLHttpRequest to get data from the server:

var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
        var myObj = JSON.parse(this.responseText);
        document.getElementById("demo").innerHTML = myObj.name;
    }
};
xmlhttp.open("GET", "json_demo.txt", true);
xmlhttp.send();

 

 

 

 

 

 

 

Tags: 
youngdeok's picture

Language

Get in touch with us

"If you would thoroughly know anything, teach it to other."
- Tryon Edwards -

Contact us