JavaScript Basics Flashcards
JavaScript Statement
Like a sentence, its one idea in JS. They end in a semi colon. One statement needs to complete before the next runs.
JavaScript Engine
It’s a powerful part of the browser that reads, understands and runs the instructions in a JavaScript program.
How do you use JavaScript in its own file?
You write a .js file with the code and then you link it to the HTML. This is basically the same thing you do with CSS.
How do you link a .js file to HTML?
This needs to be inside of the head tags of the html doc.
What is an addition assignment operator?
It is an operator that will take the value of a current variable and add a specified ammount to. It is basically shorthand for myVar = myVar + 10 into myVar += 10.
So the actual operator is +=
What are the main differences between using let vs var?
Scope.
Using var creates a variable that has function wide scope, but let has only block wide scope.
What is a JavaScript method?
Its an action that can be preformed on an object.
How do you call a method on an object?
myObjectName.toLowerCase()
This would take the string called myObjectName and convert it all to lower case.
You’d then need to put that whole method call inside of like.. console.log ( insert stuff here); to write that to the console.
What is a template literal?
Its an easier way to deal with strings. It allows you to put multiple variables inside of an output sentence so that you don’t have to concatenate tons of sections of sentences.
The template literal must be inside of the ` symbol, so like this
You can then insert variable names inside like this:
${varName}
How do you specify where you want content to be inserted into HTML using JS?
You can do this with document.querySelector()
Inside the (), you specify the HTML element you want to target, for example, document.querySelector(‘main’); would target your <main></main> element.
You can specify a tag name, class or ID here.
The JS Engine will locate the first main element that it finds. This is why it would be better to use an ID or specific identifier if there are more than one element of the same type on your page.
How do you tell the selected HTML element what content you want to send to it?
Use the inner.HTML property. So for example,
document.querySelector(‘main’).innerHTML = shoutMessage;
What is the strict equality operator and what does it do?
It is === and it compares if to values are the same. It can be used in if statements like:
if ( varX === 10 ) {
do stuff
}
The if statement will evaluate to true if varX is 10. If its not 10, it will be false.
What is the difference between the equality operator and the strict equality operator?
== does not compare data types, so (‘3’ == 3) is true, it converts the ‘3’ in string format to an interger.
The strict equality operator === would return false.
What is the logical AND operator and what does it do?
&& , it allows you to check if multiple things are true at the same time.
eg, it is snowing AND you have your fishing gear ready.
or
( age > 20 && age < 30 ) checks if age is between 20 and 30.
In order to evaluate to TRUE, both checks must be true.
What is the logical OR operator and what does it do?
|| , it checks if either arguments evaluate to true.
Will evaluate to true if either option is true.
So x = 4
if ( x < 5 || x > 9 )
X IS less than 5 but NOT greater than 9.
One of the statements is true so the overall OR comparison evaluates to true.
How do you write comments in JS?
single line: //
Multi line: /*
*/
