CODEWITHSUNDEEP
javascript
user1679941
user1679941

Reputation:

Javascript substring() returning the wrong value from my string?

I have this code:

var sequence = $stateParams.testId.length == 14 ?
               parseInt($stateParams.testId.substring(11, 2)) : 0;

What I expect is for the sequence to be set to 01 (the last two numbers). But what happens is that it returns 198.

Can someone explain why this is?

console.log($stateParams.testId) // "01198-05282-01"

console.log(sequence) // 198

Upvotes: 2

Views: 1697

Answers (3)

Tushar
Tushar

Reputation: 87203

The problem with substring() is well-explained in this answer. If you want to get the last number after -, you can use regex.

/\d+$/

Code:

var str = "01198-05282-01";

var sequence = (str.match(/\d+$/) || [])[0] || 0; // Get the last number, use 0 as default if not present
sequence = parseInt(sequence, 10);

What's wrong with substring()?

There's nothing wrong in using substring() but it has following limitations.

  1. It's static - numbers 12 and 14. One more thing to keep track of.
  2. If there are non-numeric characters at the position from 12 to 14, the result will be unexpected. However, using RegEx will give the accurate result, zero when string not end with numbers.

Upvotes: 0

Vicky Gonsalves
Vicky Gonsalves

Reputation: 11707

Here is the explaination:

Your querystring contains: "01198-05282-01"
Lets take it in a variable:

var a= "01198-05282-01";

If we substring it,

a.substring(11,2)

It will return:

"198-05282"

You have parseInt in your code, hence

parseInt("198-05282");

will return 

198

The substring() method returns a subset of a string between one index and another, or through the end of the string.

So to get the desired output you need to,

var a= "01198-05282-01";

console.log(a.substring(12,14))  //returns "01"

with parseInt(a.substring(12,14),10) //will return 1

With your code:

var sequence = $stateParams.testId.length == 14 ?
               parseInt($stateParams.testId.substring(12, 14), 10) : 0;

As

More about substring: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/String/substring

As Tushar suggessted use radix as second parameter with parseInt

The parseInt() function parses a string argument and returns an integer of the specified radix (the base in mathematical numeral systems).

radix: An integer between 2 and 36 that represents the radix (the base in mathematical numeral systems) of the above mentioned string. Specify 10 for the decimal numeral system commonly used by humans. Always specify this parameter to eliminate reader confusion and to guarantee predictable behavior. Different implementations produce different results when a radix is not specified, usually defaulting the value to 10.

Upvotes: 0

Tushar
Tushar

Reputation: 87203

String#substring works with the indexes.

The signature of the substring is

str.substring(indexStart[, indexEnd])

Note that the second parameter is the index itself and not the length of the substring.

Quoting from MDN

If indexStart is greater than indexEnd, then the effect of substring() is as if the two arguments were swapped; for example, str.substring(1, 0) == str.substring(0, 1).

So,

.substring(11, 2) is equivalent to .substring(11, 2) which will give the substring "198-05282-" and using parseInt() on it will give the output as 198.

  1. Use the second param as index, here, 14(12 + 2)
  2. Use the radix parameter to parseInt as 10 to avoid unexpected results

Code:

var str = '01198-05282-01';

var sequence = str.length == 14 ?
    parseInt(str.substring(12, 14), 10) : 0;
//                             ^^   ^^

console.log(sequence);

To get the substring using the length, use String#substr

str.substr(12, 2)

Upvotes: 1

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