# JavaScript: Round a number to a specified amount of digits

## JavaScript fundamental (ES6 Syntax): Exercise-152 with Solution

Write a JavaScript program to round a number to a specified amount of digits.

• Use Math.round() and template literals to round the number to the specified number of digits.
• Omit the second argument, decimals, to round to an integer.

Sample Solution:

JavaScript Code:

``````//#Source https://bit.ly/2neWfJ2
const round = (n, decimals = 0) => Number(`\${Math.round(`\${n}e\${decimals}`)}e-\${decimals}`);

console.log(round(1.005, 2));
console.log(round(1.05, 2));
console.log(round(1.0005, 2));
```
```

Sample Output:

```1.01
1.05
1
```

Pictorial Presentation:

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-152-1 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