doorfly doorfly - 6 months ago 15
Node.js Question

Object has no method 'reduce' error when using arguments in node.js?

Why do I get an error when using

arguments
like this?

function sum(){
return arguments.reduce(function(a,b){
console.log(a+b)
return a+b;
},0);
}

sum(1,2,3,4);


error:

/Users/bob/Documents/Code/Node/hello.js:2
return arguments.reduce(function(a,b){
^
TypeError: Object #<Object> has no method 'reduce'
at sum (/Users/bob/Documents/Code/Node/hello.js:2:19)
at Object.<anonymous> (/Users/bob/Documents/Code/Node/hello.js:8:1)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)
at startup (node.js:119:16)
at node.js:903:3


This is from Mr. Crockford's JS lectures.

Answer

arguments is not a real array, it's an "array-like" object and reduce is not a method of array-like objects. You can use reduce by passing arguments as context, like this:

[].reduce.call(arguments, function(a, b) {

});

Edit: more info on array-like objects here at the MDN.

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