1. Truthy & Falsy value
Here false,’’(empty string), “”(empty string), 0(Zero), null, undefined, NaN(Not a Number) are falsy values and anything that is not mentioned above are truthy values.
example of Truthy & falsy value
Note: if we write 0 & false in a double quotation it will return true because these are string! So don’t be confused!
2.Undefined Vs Null
Undefined is when we declare a variable and value has been not assigned yet. Null means empty or non-existence value and null should be assigned.
undefined Vs null
Here, we want access to an index of 11 which is not available in numbers. That time it gives undefined. A name variable is declared but value not assigned.
3. double equals (==) vs triple equals (===)
Double equals will check only the value equality. Double equals(==) is also called Abstract Equality Comparison.
Triple equals will check value and data-type. Triple equals(===) is also called Strict Equality Comparison.
double equals (==) vs triple equals (===)
Here, in firstExample is number and secondExample is string when checking the equality of value the answer returns true because it just checks the value not data-type!
When checking value and data-types at a time it returns false because value is equal but data-type are different.
4. 3Powerful array functions:
If any one asked a developer which array functions are powerful the answer will be most probably map, filter ,find!
- map returns us a same length of array and original array will not change
example of map()
- filter returns us a new array where passed condition is satisfied or true.
- If the passed condition is not satisfied or false then that element will be skipped.
- If there are no elements in the original array that return true then an empty array will be returned.
example of filter()
- find returns the first items in an array where passed condition is satisfied.
example of find()
The Syntax of map/filter/find:
function(currentValue, index, arr)
currentValue = Required. The value of the current element.
index = Optional. The array index of the current element.
arr = Optional. The array object the current element belongs to.
5. Array slice()
- The slice() method returns a copy of a small portion of an array into a new array.
- Where it is selected from a start value and end value.
- The start value is the index number of start & end value is the index of items in that array.
- Hence the original array will not be changed.
slice of pudding
- Suppose, when we cut a slice of pudding it has a start & end area and we get the slice before the end area. Similarly, in the example below the index start value is 2 and index end value is 5. So we will get the slice of index 2 to index 4, the value of those indexes are 13,14,15.
example of slice()
6. Array splice()
- The splice() method will add item in an array or remove item from an array.
- Hence the original array will be changed.
array.splice(start, howmany, item1, ….., itemX)
start = The index from which it will start changing the array.
howmany = The number of items to be removed.
item1, ….., itemX = The new item/items to be added to the array
example of splice()
In this example, the starting index is 2 & removed item value is 5, so from index 2 it will remove the next 5 items. We can see the original array is changed after splice().