Why can't I add an integer and variable in the console log?

Question

I'm wanting to print number + 1 in the console log but instead of adding the numbers together, it concatenates them. What am I doing wrong? For instance, if the user inputs 7, instead of getting 8, it will print 17.

let number = prompt('what is your favorite number')
if(number == 42){
  console.log("Yay! That's my favorite too!")
} else if (number < 42){
  console.log("Eh, that's OK but " + (1 + number) + " would have been better")
} else{
  console.log("LAME. That number is too large!")
}


console.log()

If a user inputs a number less than 42, it should add 1 to the entered number and print that number. However, the current code is concatenating 1 to the number.

This is because javascript is a dynamic typed language, it can convert numbers to strings based on the context, try number*1, this is clearly a number operation so javascript will treat number as a number and not as a string. — x13
– x13, Commented May 8, 2019 at 14:07

6502 · Accepted Answer · 2019-05-08 14:06:30Z

1

prompt returns a string... you need to convert it to a number, for example with

number = +number;

before using it as a number

answered May 8, 2019 at 14:06

6502

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Comments

Rahul · Accepted Answer · 2019-05-08 14:07:51Z

1

You can use as it will consider it a string while performing arithmatic operations

number = Number(number)

You will get more details about this wrapper object here.

answered May 8, 2019 at 14:07

Rahul

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obscure · Accepted Answer · 2019-05-08 14:07:42Z

0

That is because prompt returns a string. So if you enter 21 for example and add 1 the result will be 211.

You need to convert number to a number right after prompt like:

number = parseInt(number);

answered May 8, 2019 at 14:07

obscure

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ljbc1994 · Accepted Answer · 2019-05-08 14:15:11Z

0

It's because the value returned from executing prompt is a string rather than a number. You need to parse the string into a number using parseInt[1], or if you're allowing floats parseFloat[2].

For example:

let response = prompt('what is your favorite number')
let number = parseInt(response, 10) // Convert response into a string
if(number == 42){
  console.log("Yay! That's my favorite too!")
} else if (number < 42){
  console.log("Eh, that's OK but " + (1 + number) + " would have been better")
} else{
  console.log("LAME. That number is too large!")
}


console.log()

References

[1] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt

[2] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseFloat

edited May 8, 2019 at 14:15

answered May 8, 2019 at 14:08

ljbc1994

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