Rxjs map only first emition

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

asked Nov 21 '18 at 0:43

Rachid Oussanaa

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

add a comment |

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

asked Nov 21 '18 at 0:43

Rachid Oussanaa

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

add a comment |

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

asked Nov 21 '18 at 0:43

Rachid Oussanaa

4,73183862

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

asked Nov 21 '18 at 0:43

Rachid Oussanaa

4,73183862

asked Nov 21 '18 at 0:43

Rachid Oussanaa

4,73183862

asked Nov 21 '18 at 0:43

Rachid Oussanaa

4,73183862

asked Nov 21 '18 at 0:43

Rachid Oussanaa

4,73183862

asked Nov 21 '18 at 0:43

Rachid Oussanaa

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

add a comment |

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

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

add a comment |

2 Answers
2

active

oldest

votes

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.

answered Nov 21 '18 at 9:51

cartant

37.6k785118

add a comment |

Use first operator or take(1)

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

const example = source.pipe(first());

answered Nov 21 '18 at 9:19

Fan Cheung

2,8621419

add a comment |

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

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.

answered Nov 21 '18 at 9:51

cartant

37.6k785118

add a comment |

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.

answered Nov 21 '18 at 9:51

cartant

37.6k785118

add a comment |

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.

answered Nov 21 '18 at 9:51

cartant

37.6k785118

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.

answered Nov 21 '18 at 9:51

cartant

37.6k785118

answered Nov 21 '18 at 9:51

cartant

37.6k785118

answered Nov 21 '18 at 9:51

cartant

37.6k785118

answered Nov 21 '18 at 9:51

cartant

37.6k785118

add a comment |

Use first operator or take(1)

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

const example = source.pipe(first());

answered Nov 21 '18 at 9:19

Fan Cheung

2,8621419

add a comment |

Use first operator or take(1)

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

const example = source.pipe(first());

answered Nov 21 '18 at 9:19

Fan Cheung

2,8621419

add a comment |

Use first operator or take(1)

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

const example = source.pipe(first());

answered Nov 21 '18 at 9:19

Fan Cheung

2,8621419

Use first operator or take(1)

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

const example = source.pipe(first());

answered Nov 21 '18 at 9:19

Fan Cheung

2,8621419

answered Nov 21 '18 at 9:19

Fan Cheung

2,8621419

answered Nov 21 '18 at 9:19

Fan Cheung

2,8621419

answered Nov 21 '18 at 9:19

Fan Cheung

2,8621419

add a comment |

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