Typescript string | string[] find the array length

Question

I am finding the length of string|string[] , I have variable as a data type of var stepData : string | string[] . Some times I am getting a single string value , also possible to get the list of string . Using the length of array I am doing some other operation. In my code I am doing some for loop function using that stepData.length . Here the sample my code

const stepData: string|string[] = this.$stateParams.stepData;

 // Here two possible length value I am getting 
 // If the stepData is string[] get length of array value 
 // If the stepData is string  get the length of string
 // The `lengthVar` depends on below for loop

 if (stepData.length > 0) {
        var lengthVar = stepData.length;
     for (var i = 0; i < lengthVar; i++) {
          // Inside im writing some ajax call
     }
 }

How to find the exact array length of stepData I want array value only using I am calling AJAX method inside . If any suggest I am trying any wrong or give ur valuable suggestions please.

it's not very clear what you want. do you want to deffrintiate between the two possible types of stepData? if so, how? and what's this dataId? please explain what you want better. — Nitzan Tomer
– Nitzan Tomer, Commented Jul 5, 2016 at 19:30
What's the matter with .length ? That does exactly what you want on both types. — AlexG
– AlexG, Commented Jul 5, 2016 at 19:34
Exactly I want the stepData , when its string and when its string[] finding the length of array i am calling AJAX inside for loop — SakthiSureshAnand
– SakthiSureshAnand, Commented Jul 5, 2016 at 19:35
No, If I am getting string[] I got diffrent length , if string i am getting the length of string value which is inside the stepData . But below for loop executed that much time called , if the value is string. This is the problem I am facing — SakthiSureshAnand
– SakthiSureshAnand, Commented Jul 5, 2016 at 19:37
@AlexG Below for loop I am executing only length of array only , if the value is string . Its excuted more times created more number of data inside Database, — SakthiSureshAnand
– SakthiSureshAnand, Commented Jul 5, 2016 at 19:40

AlexG · Accepted Answer · 2016-07-05 19:51:12Z

1

Just do something like:

const _stepData = (typeof stepData === 'string') ? [stepData] : stepData;

then iterate it as an Array. More consistent, less bugs.

answered Jul 5, 2016 at 19:51

AlexG

4,1151 gold badge26 silver badges19 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Nitzan Tomer · Accepted Answer · 2016-07-05 19:51:44Z

1

You're questions is very unclear, but I'll take a guess that you're asking how to know whether the value in stepData is a string or string[], if that the case then:

if (typeof stepData === "string") {
    // stepData is a string
} else { 
    // stepData is a string[]
}

or

if (stepData instanceof Array) {
    // stepData is a string[]
} else { 
    // stepData is a string
}

You can make your stepData not a const and then:

let stepData: string|string[] = this.$stateParams.stepData;

if (typeof stepData === "string") {
    stepData = [stepData];
}

// now stapData is string[]

answered Jul 5, 2016 at 19:51

Nitzan Tomer

166k51 gold badges330 silver badges307 bronze badges

Comments

Mattias Buelens · Accepted Answer · 2016-07-05 19:51:47Z

1

From your comment on the question:

Inside for I am iterating stepData.length . So If its string only one time I should iterate ,If its string[] I should find the length of string array that much time I iterate

In that case, your code must be able to differentiate between string and string[] with a check at runtime. A simple check to differentiate between the two would be typeof stepData === "string", which will be true for strings but false for string[]s.

if (typeof stepData === "string") {
    // here stepData is a string
} else {
    // here stepData is a string[]
}

answered Jul 5, 2016 at 19:51

Mattias Buelens

20.2k4 gold badges47 silver badges52 bronze badges

Comments

Reginaldo Camargo Ribeiro · Accepted Answer · 2016-07-06 12:33:03Z

1

If you want to know if some variable is a string or string[] you could use the keyword instanceof:

if(stepData instanceof Array<string>) {
...
} else {
...
}

or

if(typeof stepData === "string") {
...
} else {
...
}

edited Jul 6, 2016 at 12:33

answered Jul 5, 2016 at 19:54

Reginaldo Camargo Ribeiro

7684 silver badges15 bronze badges

1 Comment

Nitzan Tomer Over a year ago

you can't use instanceof on string (or String), and checking if it's "object" doesn't get him so far as it can be a lot of things

Collectives™ on Stack Overflow

Typescript string | string[] find the array length

4 Answers 4

Comments

Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related