javascript - How to determine parameter list of callback functions -

in d3.js, time pass callback function argument, e.g. in delay() below:

d3.select('body').selectall('div')   .data(distances)   .enter()   .append('div')   .html('.')   .style('width', '10px')   .style('opacity', 0)   .transition()     .delay(function(d, i) { return * 1000 }) 

question: how know callback function shall have 2 parameters: d , i. , in document specify 'd' should correspond datum , 'i' correspond index?

my question not limited d3.js js convention in general. e.g. in angular.js, found similar thing. e.g. in callback function passed then() below:

// simple request example: $http({   method: 'get',   url: '/someurl' }).then(function successcallback(response) {     // callback called asynchronously     // when response available   }, function errorcallback(response) {     // called asynchronously if error occurs     // or server returns response error status.   }); 

how know (i.e. document specifies ) callback function supposed take argument , argument correspond response?

my question not limited d3.js js convention in general.

it has documented api method you're passing callback to. there's no other way know arguments callback called with — or when called, (if anything) it's expected return, etc.

for d3 example, it's defined in delay documentation:

otherwise, if delay function, function evaluated each selected element (in order), being passed current datum d , current index i, this context current dom element.

for angularjs example, then promise function, documented here:

the promise api

...

methods

• then(successcallback, errorcallback, notifycallback) – regardless of when promise or resolved or rejected, calls 1 of success or error callbacks asynchronously result available. callbacks called single argument: result or rejection reason. additionally, notify callback may called 0 or more times provide progress indication, before promise resolved or rejected.