# JavaScript: Check if the given number falls within the given range

## JavaScript fundamental (ES6 Syntax): Exercise-217 with Solution

Write a JavaScript program to check if the given number falls within the given range.

• Use arithmetic comparison to check if the given number is in the specified range.
• If the second argument, end, is not specified, the range is considered to be from 0 to start.

Sample Solution:

JavaScript Code:

``````//#Source https://bit.ly/2neWfJ2
const inRange = (n, start, end = null) => {
if (end && start > end) end = [start, (start = end)][0];
return end == null ? n >= 0 && n < start : n >= start && n < end;
};
console.log(inRange(3, 2, 5));
console.log(inRange(3, 4));
console.log(inRange(2, 3, 5));
console.log(inRange(3, 2));
```
```

Sample Output:

```true
true
false
false
```

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-217-1 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