JavaScript: Initialize and fill an array with the specified values
JavaScript fundamental (ES6 Syntax): Exercise-213 with Solution
Write a JavaScript program to initialize and fill an array with the specified values.
- Use Array.from() to create an array of the desired length, Array.prototype.fill() to fill it with the desired values.
- Omit the last argument, val, to use a default value of 0.
Sample Solution:
JavaScript Code:
//#Source https://bit.ly/2neWfJ2
const initializeArrayWithValues = (n, val = 0) => Array(n).fill(val);
console.log(initializeArrayWithValues(5, 2));
console.log(initializeArrayWithValues(4, 0));
Sample Output:
[2,2,2,2,2] [0,0,0,0]
Pictorial Presentation:
Flowchart:

Live Demo:
See the Pen javascript-basic-exercise-213-1 by w3resource (@w3resource) on CodePen.
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JavaScript: Tips of the Day
Checking if a key exists in a JavaScript object?
Checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined?
var obj = { key: undefined }; obj["key"] !== undefined // false, but the key exists!
You should instead use the in operator:
"key" in obj // true, regardless of the actual value
If you want to check if a key doesn't exist, remember to use parenthesis:
!("key" in obj) // true if "key" doesn't exist in object !"key" in obj // ERROR! Equivalent to "false in obj"
Or, if you want to particularly test for properties of the object instance (and not inherited properties), use hasOwnProperty:
obj.hasOwnProperty("key") // true
Checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined? var obj = { key: undefined }; obj["key"] !== undefined // false, but the key exists! You should instead use the in operator: "key" in obj // true, regardless of the actual value If you want to check if a key doesn't exist, remember to use parenthesis: !("key" in obj) // true if "key" doesn't exist in object !"key" in obj // ERROR! Equivalent to "false in obj" Or, if you want to particularly test for properties of the object instance (and not inherited properties), use hasOwnProperty: obj.hasOwnProperty("key") // true For performance comparison between the methods that are in, hasOwnProperty and key is undefined.
Ref: https://bit.ly/2CFNp1X
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