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World Wide Pond Devlpmnt/Design > IES: JS-deck 5 > Flashcards

IES: JS-deck 5 Flashcards

1
Q

JS “var”

A
  • JS keyword
  • JS significant: avoid in variable/function names
  • Used to declare a variable,
  • Example
 var  fruits = ["apple", "banana", "orange"];
var age=22;
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2
Q

JS “void”

A
  • JS keyword
  • JS significant: avoid for variable/function names
  • used to evaluates an expression and returns undefined. A void operator is frequently used to get the undefined primitive value.
  • Syntax
    void expression;
  • Example
void 0; // Returns undefined
void (1 + 2); // Returns undefined
void console.log("Hello"); // Prints "Hello" to the console, but returns undefined
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3
Q

JS “volatile”

A
  • JS keyword
  • JS significant: In JavaScript, the volatile keyword is not implemented and has been reserved for future use.
  • In Java, the volatile keyword is a modifier - ensures attribute’s value is the same from all threads: JS is single threaded.
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4
Q

JS “while”

A
  • JS keyword
  • JS significant: avoid in variable/function names
  • Used for while loop, while loop executes the block of code until the condition is true.
  • Example
    ~~~
    var a=1;
    while(a <= 10)
    {
    document.write(“loop is running for “ + a + “times</p>”);
    a++;
    }
    ~~~
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5
Q

JS “with”

A
  • JS keyword
  • JS significant: avoid in variable/function names
  • Used for iterating, just, in short, it is shortened for iteration.
  • Example
var  fruits = ["apple", "banana", "orange"];
for ( var i = fruits.length; i--; ) {
with ({ no : i }) {
link.onclick = function() {
alert(no);
};
}
}
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6
Q

JS “yield”

A
  • JS keyword
  • JS significant: avoid for variable/function names
  • Used to pause and resume a generator function. The generator function is the same as a normal function but for returning a value in place of return it uses yield keyword.
  • Example
function* iter( a ) {
while (a < 4) {
yield a++;
}
}
const i = iter ( 1 );
console.log(i.next().value);  //return 1
console.log(i.next().value);  //return 2
console.log(i.next().value);  //return 3
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7
Q

JS Array

A
  • JS object
  • JS significant: avoid for variable/function names
  • one of most commonly used data types
  • An ordered value list identified by an index starting at zero
  • Create an array:
    array literal
    let fruits = ["apple", "banana", "orange"];
    Array constructor
    let numbers = new Array(1, 2, 3, 4, 5);
  • Access an array element:
    Using its index
console.log(fruits[0]); // Output: "apple"
console.log(numbers[2]); // Output: 3
  • Modifying array elements:
    By assigning a new value to its index
fruits[1] = "grape";
console.log(fruits); // Output: ["apple", "grape", "orange"]
  • JS built-in methods to manipulate arrays
    push(), pop(), unshift(), shift(), splice(), concat(), slice(), indexOf(), forEach(), map(), filter(), reduce(),
    Array manipulation Example
let colors = ["red", "green", "blue"];

colors.push("yellow"); // Add "yellow" to the end
console.log(colors); // Output: ["red", "green", "blue", "yellow"]

colors.pop(); // Remove the last element
console.log(colors); // Output: ["red", "green", "blue"]

colors.forEach(function(color) {
  console.log(color); // Output: "red", "green", "blue"
});
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8
Q

JS Date

A
  • JS Object
  • JS significant: avoid for variable/function names
  • Date objects are static: The computer clock is ticking; date objects are not.
  • There are nine ways to create a new date object:
    1. new Date()
    2. new Date(date string)
    3. new Date(year,month)
    4. new Date(year,month,day)
    5. new Date(year,month,day,hours)
    6. new Date(year,month,day,hours,minutes)
    7. new Date(year,month,day,hours,minutes,seconds)
    8. new Date(year,month,day,hours,minutes,seconds,ms)
    9. new Date(milliseconds)
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9
Q

JS eval

A
  • JS Method
  • JS significant: avoid for variable/function names
  • evaluates or executes its argument.
  • If the argument is an expression, it evaluates the expression.
  • If it’s one or more statements, it executes the statements.
  • Syntax
    eval(string);
  • Example
    function func() {
    // Original string
    let a = 2;
    let b = 2;
    // Finding the sum
    let value = eval(new String(a + b));
    console.log(value);
    }
  • Output
    [String: ‘4’]
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10
Q

JS function

A
  • JS Object, Property, or Method
  • JS significant: avoid for variable/function names
  • block of code designed to perform a specific task. It’s a reusable piece of code that can be called multiple times
  • Examples
    Simple 
function greet(name) {
  console.log("Hello, " + name + "!");
}
greet("John"); // Output: Hello, John!

With return value

function add(x, y) {
  return x + y;
}
let sum = add(5, 3); 
console.log(sum); // Output: 8

Anonymous function

const square = function(x) {
  return x * x;
}
console.log(square(4)); // Output: 16

Arrow function (ES6 syntax)

const multiply = (x, y) => x * y;
console.log(multiply(2, 6)); // Output: 12
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11
Q

JS hasOwnProperty

A
  • JS Method
  • JS significant: avoid for variable/function names
  • used to check if an object has a specific property as its own property (not inherited from its prototype chain).
  • Example
const person = {
  name: "John",
  age: 30
};
console.log(person.hasOwnProperty("name")); // true
console.log(person.hasOwnProperty("age")); // true
console.log(person.hasOwnProperty("toString")); // false (inherited from Object.prototype)
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12
Q

JS Infinity

A
  • JS “Global” Method
  • JS significant: avoid for variable/function names
  • Infinity is a number that represents positive infinity.
    A number reaches Infinity when it exceeds the upper limit for a number: (1.797693134862315E+308.)
  • Example
let x = 1.797693134862315E+308;
let y = x * 1.001;
  • -Infinity represents negative infinity.
    A number reaches -Infinity when it exceeds the lower limit for a number: (-1.797693134862316E+308.)
  • Example
let x = -1.797693134862316E+308;
let y = x * 1.001;
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13
Q

JS isFinite

A
  • JS Method
  • JS significant: avoid for variable/function names
  • determines whether the passed value is a finite number.
  • Returns false if positive infinity, negative infinity, or NaN
  • Syntax
    Number.isFinite(value);
  • Example
    Number.isFinite(123); // true
    Number.isFinite(-1.23); // true
    Number.isFinite(Infinity); // false
    Number.isFinite(-Infinity); // false
    Number.isFinite(NaN); // false
    Number.isFinite(“123”); // false (because it’s a string, not a number)
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14
Q

JS isNaN

A
  • JS Method
  • JS significant: avoid for variable/function names
  • Determines whether a value is NaN( “Not a Number” ): Return or output is either “true” or “false”
  • Important
    1. isNaN() first attempts to convert the given value to a number. If the conversion results in NaN, it returns true. This can lead to unexpected results.
    2. Number.isNaN() is a more precise alternative that doesn’t perform type coercion. It only returns true if the value is exactly the NaN value.
  • Examples
isNaN(NaN); // true
isNaN(Number.NaN); // true
isNaN(0 / 0); // true
isNaN(123); // false
isNaN("123"); // false, because "123" can be converted to a number
isNaN("Hello"); // true, because "Hello" cannot be converted to a number
isNaN(true); // false, because true is converted to 1
isNaN(false); // false, because false is converted to 0
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15
Q

JS isPrototypeOf

A
  • JS Method
  • JS significant: avoid for variable/function names
  • Determines if an object is in the prototype chain of another object
  • Definition
    Object.prototype.isPrototypeOf(object)
  • Examples new
function Person(name) {
  this.name = name;
}
const person1 = new Person("Alice");
console.log(Person.prototype.isPrototypeOf(person1)); // true
console.log(Object.prototype.isPrototypeOf(person1)); // true

```

const obj1 = { a: 1 };
const obj2 = Object.create(obj1);
~~~
console.log(obj1.isPrototypeOf(obj2)); // true

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16
Q

JS length

A
  • JS Property
  • JS significant: avoid for variable/function names
  • Determine the size of different data types:
    1. Strings: returns the number of characters in.
let message = "Hello, world!";
console.log(message.length); // Output: 13
  1. Arrays: returns to the number of elements in.
let fruits = ["apple", "banana", "orange"];
console.log(fruits.length); // Output: 3
  1. Objects: (not directly applicable). However, Object.keys() acquires the properties number in an object.
let person = { name: "John", age: 30, city: "New York" };
console.log(Object.keys(person).length); // Output: 3
  1. Functions: returns the number of parameters expected
function sum(a, b) {
  return a + b;
}
console.log(sum.length); // Output: 2
17
Q

JS Math

A
  • JS Object
  • JS significant: avoid for variable/function names
  • Has no constructor
  • Is static
  • Methods & properties can be used without creating this first
  • Examples
    // Calculating the area of a circle
const radius = 5;
const area = Math.PI * Math.pow(radius, 2);
console.log("The area of the circle is:", area);

// Generating a random number between 1 and 10

const randomNumber = Math.floor(Math.random() * 10) + 1;
console.log("Random number:", randomNumber);

// Finding the square root of a number

const number = 25;
const squareRoot = Math.sqrt(number);
console.log("The square root of", number, "is:", squareRoot);
18
Q

JS NaN

A
  • JS Global Property
  • JS significant: avoid for variable/function names
  • Short for “Not-a-Number”
  • Not a legal number
  • Global NaN property is the same as the Number. Nan property
  • Examples
    // Examples of operations that result in NaN
let result1 = 0 / 0; 
let result2 = Math.sqrt(-1);
let result3 = parseInt("Hello");
19
Q

JS name

A
  • JS Object, Property, or Method
  • JS significant: avoid for variable/function names
  • Accesses the name of various elements like functions, objects, and HTML elements.
  • Examples
    1. Function Name
function greet() {
  console.log("Hello, world!");
}
console.log(greet.name); // Output: "greet"
  1. Object Property
const person = {
  name: "John Doe",
  age: 30
};
console.log(person.name); // Output: "John Doe"
  1. HTML Element Name
<input type="text" name="username">
const usernameInput = document.querySelector("input[name='username']");
console.log(usernameInput.name); // Output: "username"
  1. Computed Property Name
    const propertyName = “city”;
    const address = {
    [propertyName]: “New York”
    };

console.log(address.city); // Output: “New York”

20
Q

JS Number

A
  • JS Primitive value or Object
  • JS significant: avoid for variable/function names
  • the Number data type represents both integers and floating-point numbers: JS does not define different types of numbers, like integers, short, long, floating-point etc.
  • Always stored as double precision floating point numbers, following international IEEE 754 standard.
  • Examples
    // Creating number variables
let x = 10;
let y = 3.14;

// Performing arithmetic operations

let sum = x + y;
let difference = x - y;
let product = x * y;
let quotient = x / y;
let remainder = x % y;

// Using built-in methods

let rounded = Math.round(y);
let max = Math.max(x, y);
let min = Math.min(x, y);
let squareRoot = Math.sqrt(x);

// Converting numbers to strings
let numString = x.toString();
// Checking if a value is a number
let isNumber = Number.isInteger(x);

console.log("Sum:", sum);
console.log("Difference:", difference);
console.log("Product:", product);
console.log("Quotient:", quotient);
console.log("Remainder:", remainder);
console.log("Rounded:", rounded);
console.log("Max:", max);
console.log("Min:", min);
console.log("Square Root:", squareRoot);
console.log("Number as String:", numString);
console.log("Is x a number?", isNumber);

World Wide Pond Devlpmnt/Design (53 decks)

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