Rxjs map only first emition












0















Is there an operator that can let me map just the first emit ?



something like



import { from } from 'rxjs';

import { mapFirst } from 'rxjs/operators';



const source = from([1, 2, 3, 4, 5]);

const example = source.pipe(mapFirst(val => val + 10));

//output: 11,2, 3, 4, 5





rxjs







share|improve this question


















  • 2





    Check the index map((value, index) => { if (index === 0) ... }

    – cartant
    Nov 21 '18 at 2:04











  • @cartant thanks but I knew I could do this, I was hoping for some home baked operator, for the sake of a nicer syntax :)

    – Rachid Oussanaa
    Nov 21 '18 at 9:37
















0















Is there an operator that can let me map just the first emit ?



something like



import { from } from 'rxjs';

import { mapFirst } from 'rxjs/operators';



const source = from([1, 2, 3, 4, 5]);

const example = source.pipe(mapFirst(val => val + 10));

//output: 11,2, 3, 4, 5





rxjs







share|improve this question


















  • 2





    Check the index map((value, index) => { if (index === 0) ... }

    – cartant
    Nov 21 '18 at 2:04











  • @cartant thanks but I knew I could do this, I was hoping for some home baked operator, for the sake of a nicer syntax :)

    – Rachid Oussanaa
    Nov 21 '18 at 9:37














0












0








0








Is there an operator that can let me map just the first emit ?



something like



import { from } from 'rxjs';

import { mapFirst } from 'rxjs/operators';



const source = from([1, 2, 3, 4, 5]);

const example = source.pipe(mapFirst(val => val + 10));

//output: 11,2, 3, 4, 5





rxjs







share|improve this question














Is there an operator that can let me map just the first emit ?



something like



import { from } from 'rxjs';

import { mapFirst } from 'rxjs/operators';



const source = from([1, 2, 3, 4, 5]);

const example = source.pipe(mapFirst(val => val + 10));

//output: 11,2, 3, 4, 5





rxjs




rxjs






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Nov 21 '18 at 0:43









Rachid OussanaaRachid Oussanaa

4,73183862




4,73183862








  • 2





    Check the index map((value, index) => { if (index === 0) ... }

    – cartant
    Nov 21 '18 at 2:04











  • @cartant thanks but I knew I could do this, I was hoping for some home baked operator, for the sake of a nicer syntax :)

    – Rachid Oussanaa
    Nov 21 '18 at 9:37














  • 2





    Check the index map((value, index) => { if (index === 0) ... }

    – cartant
    Nov 21 '18 at 2:04











  • @cartant thanks but I knew I could do this, I was hoping for some home baked operator, for the sake of a nicer syntax :)

    – Rachid Oussanaa
    Nov 21 '18 at 9:37








2




2





Check the index map((value, index) => { if (index === 0) ... }

– cartant
Nov 21 '18 at 2:04





Check the index map((value, index) => { if (index === 0) ... }

– cartant
Nov 21 '18 at 2:04













@cartant thanks but I knew I could do this, I was hoping for some home baked operator, for the sake of a nicer syntax :)

– Rachid Oussanaa
Nov 21 '18 at 9:37





@cartant thanks but I knew I could do this, I was hoping for some home baked operator, for the sake of a nicer syntax :)

– Rachid Oussanaa
Nov 21 '18 at 9:37












2 Answers
2






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oldest

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1
















If you want to write a user-land operator to do it:



import { OperatorFunction } from "rxjs";

import { map } from "rxjs/operators";



function mapFirst<T, R>(selector: (value: T) => R): OperatorFunction<T, T | R> {

    return map<T, T | R>((value, index) => (index === 0) ? selector(value) : value);

}


And you'd use it as you have in your question.






share|improve this answer































    0














    Use first operator or take(1)



    const source = from([1, 2, 3, 4, 5]);
    
const example = source.pipe(first());





    share|improve this answer























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      2 Answers
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      active

      oldest

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      2 Answers
      2






      active

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      1
















      If you want to write a user-land operator to do it:



      import { OperatorFunction } from "rxjs";
      
import { map } from "rxjs/operators";
      

      
function mapFirst<T, R>(selector: (value: T) => R): OperatorFunction<T, T | R> {
      
    return map<T, T | R>((value, index) => (index === 0) ? selector(value) : value);
      
}


      And you'd use it as you have in your question.






      share|improve this answer




























        1
















        If you want to write a user-land operator to do it:



        import { OperatorFunction } from "rxjs";
        
import { map } from "rxjs/operators";
        

        
function mapFirst<T, R>(selector: (value: T) => R): OperatorFunction<T, T | R> {
        
    return map<T, T | R>((value, index) => (index === 0) ? selector(value) : value);
        
}


        And you'd use it as you have in your question.






        share|improve this answer


























          1












          1








          1









          If you want to write a user-land operator to do it:



          import { OperatorFunction } from "rxjs";
          
import { map } from "rxjs/operators";
          

          
function mapFirst<T, R>(selector: (value: T) => R): OperatorFunction<T, T | R> {
          
    return map<T, T | R>((value, index) => (index === 0) ? selector(value) : value);
          
}


          And you'd use it as you have in your question.






          share|improve this answer















          If you want to write a user-land operator to do it:



          import { OperatorFunction } from "rxjs";
          
import { map } from "rxjs/operators";
          

          
function mapFirst<T, R>(selector: (value: T) => R): OperatorFunction<T, T | R> {
          
    return map<T, T | R>((value, index) => (index === 0) ? selector(value) : value);
          
}


          And you'd use it as you have in your question.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Nov 21 '18 at 9:51









          cartantcartant

          37.6k785118




          37.6k785118

























              0














              Use first operator or take(1)



              const source = from([1, 2, 3, 4, 5]);
              
const example = source.pipe(first());





              share|improve this answer




























                0














                Use first operator or take(1)



                const source = from([1, 2, 3, 4, 5]);
                
const example = source.pipe(first());





                share|improve this answer


























                  0












                  0








                  0







                  Use first operator or take(1)



                  const source = from([1, 2, 3, 4, 5]);
                  
const example = source.pipe(first());





                  share|improve this answer













                  Use first operator or take(1)



                  const source = from([1, 2, 3, 4, 5]);
                  
const example = source.pipe(first());






                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered Nov 21 '18 at 9:19









                  Fan CheungFan Cheung

                  2,8621419




                  2,8621419






























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