Data Types Flashcards
1
Q
How are methods added to primitive data types?
A
- “object wrappers” are created for each primitive data type temporarily
- which provide an extra set of methods
2
Q
How are “normal” numbers stored in JS?
A
- 64-bit format IEEE-754
- double-precision floating-point
- min is -2^53 and max is 2^53
3
Q
Why does 0.1 + 0.2 equal 0.30000000000000004 in JS?
A
- 0.1 and 0.2 are endless fractions in binary
4
Q
How can we convert values like 12pt or 100px to numbers?
A
- parseInt / parseFloat
5
Q
How can we access characters in JS strings?
A
- str[index]
- str.charAt(index)
- iterable via for (let char of string)
6
Q
How can we get a substring?
A
- slice(start, end)
- exclusive end
- allows negatives
7
Q
Performance of pop/push VS. shift/unshift on arrays?
A
- pop/push fast
- shift/unshift slow
8
Q
How to loop over elements in array?
A
- for (let elem of arr)
9
Q
What happens if you compare (==) an array with a primitive?
A
- array (object) gets converted into a primitive
10
Q
How can we get a subarray?
A
- slice(state, end)
- exclusive end
- allows negatives
11
Q
How does arr.sort() behave?
A
- sorts array in-place
- default converts elements to strings
12
Q
How can we check if value is an array?
A
- Array.isArray()
- because using typeof returns object
13
Q
What are iterables and iterators in JS?
A
- basically objects that can be used in for..of loops
- must implement a method named Symbol.iterator
- result of objSymbol.iterator is an iterator
- An iterator must have the method named next() that returns an object {done: Boolean, value: any}, here done:true denotes the end of the iteration process, otherwise the value is the next value.
14
Q
What are array-likes in JS?
A
- objects that have indexed properties and length
15
Q
How do Maps and Objects differ?
A
- both are used for storing keyed collections
- Maps allow keys of any type, in contrast to objects where keys get converted to strings
- size property method
