IES: JS-deck 2 Flashcards
1
Q
JS function
A
- JS is case-sensitive
- Typically, expressions may be enclosed in ()
- JS coding may include keywords, operators, values -fixed and variable-, and expressions -which are basically a mix of all, sometimes, and may equal a single value.
- JS explanatory comments may be added in specific fashion
- For consistency, stick with either (‘) or (“) with string literals in your code
2
Q
JS explanatory comments
A
- “comment-out” lines of code to prevent their execution when debugging code
- shootCharacter sequences may be placed in code without execution: following a “
//” (on the same line) or between “/*” and “*/” (for one or more lines) - when comment-out coding is used, included character sequences are ignored by any code reader
- Good practice: adding explanatory comments makes your JS code more understandable to others as well as yourself, later
3
Q
JS “abstract”
A
- JS does not have a built-in abstract keyword
- JS significant: avoid in variable/function names
- In JavaScript, there is no abstract keyword
- JS: achieved using abstract classes & interfaces.
- fundamental concept in object-oriented programming (OOP)
- hiding the implementation details of an object and exposing only the essential features
4
Q
JS “arguments”
A
- JS keyword
- JS significant: avoid in variable/function names
- Represents the list of parameters passed to the function when calling the function.
- Example
~~~
const func = function(p1, p2, p3) {
const param = Array.from(arguments);
console.log(param) // [11, 22, 33]
}
func(11, 22, 33);
~~~
5
Q
JS “await”
A
- JS keyword
- JS significant: avoid in variable/function names
- Used to wait for javascript until the Promise returns its result.
- Ex’s.
1.)
~~~
async function fun() {
let promise = new Promise((resolve, reject) => {
setTimeout(() => resolve(“ yes, it is done!”), 100)
});
~~~
2.)
~~~
let res = await promise; // wait until the promise returns us a value
alert(result); // output give yes, it is done
}
};
fun();
~~~
6
Q
JS “boolean”
A
- JS keyword
- JS significant: avoid in variable/function names
- JS represents a data type that can have one of two values: true or false.
7
Q
JS “break”
A
- JS keyword
- JS significant: avoid in variable/function names
- used into a loop to break or stop the execution of the loop.
- Example
~~~
for(var a=0; a<=10; a++) {
if(a == 5)
break;
document.write(“The loop is running for “ + a + “ times”);
}
~~~
8
Q
JS “byte”
A
- JS keyword
- JS significant: avoid in variable/function names
- JS: a group of 8 bits. A bit is the most basic unit and can be either 1 or 0
- not just 8 values between 0 and 1, but 256 (2 to the 8th power)) different combinations (rather permutations) ranging from 00000000 via e.g. 01010101 to 11111111 . Thus, one byte can represent a decimal number between 0(00) and 255.
9
Q
JS “case”
A
- JS keyword
- JS significant: avoid in variable/function names
- Used in a switch-case construct, where the value of an expression compares with the case clause value and executes the statements associated with the case whose case value is matched.
- Example
~~~
var date = new Date();
switch(date.getDay()) {
case 6:
alert(“This is weekend.”);
break;
case 0:
alert(“This is weekend.”);
default:
alert(“Looking for a weekend.”);
break;
}
~~~
10
Q
JS “catch”
A
- JS keyword
- JS significant: avoid in variable/function names
- Again used in exception handling to handle the error.
- Example
~~~
Var i=1
try {
if(i == “”) throw “is Empty”;
if(x > 0) throw “positive”;
if(x < 0) throw “negative”;
}
catch(msg) {
message.innerHTML = “ Input “ + msg;
}
~~~
11
Q
JS “char”
A
- JS keyword
- JS significant: avoid in variable/function names
- reserved keyword in JavaScript that is reserved for “future” use.
- JavaScript doesn’t have a dedicated char data type.
- JS uses
stringdata type for single characters and character sequences - Strings in JavaScript are immutable: Once created, cannot be modified
- Examples
1. Access character in a string using its index, which starts from 0
~~~
let str = “Hello”;
let firstChar = str[0]; // firstChar will be ‘H’
~~~
OR
2. Create a string containing a single character using single or double quotes.
~~~
let singleChar = ‘a’;
~~~
12
Q
JS “class*”
A
- JS keyword
- JS significant: avoid in variable/function names
- Used to define a class.
- Example
~~~
public class Employee {
public String efn = “Joseph”;
public String eln = “Doe”;
}
~~~
13
Q
JS “const”
A
- JS keyword
- JS significant: avoid in variable/function names
- Used to define a constant variable and that cannot be farther reassigned.
- Example
const age=22;
14
Q
JS “continue”
A
- JS keyword
- JS significant: avoid in variable/function names
- Used into a loop to continue the loop and skip the following statements inside the loop.
- Example
~~~
for(var a=0; a<=10; a++) {
if(a == 5)
continue;
document.write(“The loop is running for “ + a + “ times”);
}
~~~
15
Q
JS “debugger”
A
- JS keyword
- JS significant: avoid in variable/function names
- Used to stop the execution of javascript code and call debugging function if define. Debugger keyword word the same as the break.
- Example
~~~
var prod = 10 * 10;
debugger;
document.getElementbyId(“id”).innerHTML = prod;
~~~
