Check function parameters for existence and type in JavaScript -

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supposed have function defined such as:

var x = function (options, callback) { /* ... */ }

options needs have properties foo , bar, foo shall of type number, , bar of type string.

so, basically, check using following code:

var x = function (options, callback) {   if (!options) { throw new error('options missing.'); }   if (!options.foo) { throw new error('foo missing.'); }   if (!options.bar) { throw new error('bar missing.'); }   if (!callback) { throw new error('callback missing.'); }   // ... }

but checks existence, not yet correct types. of course can add further checks, becomes lengthy, , not readable. once start talking optional parameters, gets mess, parameter-shifting , on …

what best way deal (supposed want check it)?

update

to clarify question: know there typeof operator, , know how deal optional parameters. have these checks manually, , - sure - not best can come with.

the goal of question was: there ready-made function / library / whatever can tell expecting 5 parameters of specific types, mandatory, optional, , function / library / whatever checks , mapping you, comes down one-liner?

basically, such as:

var x = function (options, callback) {   verifyargs({     options: {       foo: { type: 'number', mandatory: true },       bar: { type: 'string', mandatory: true }     },     callback: { type: 'function', mandatory: false }   });   // ... };

javascript has typeof

console.log( typeof '123' ); // string console.log( typeof 123 ); // number console.log( typeof undefinedvar); // undefined   var x = function (options, callback) {   if (typeof options =='undefined' { throw new error('options missing.'); }   if (typeof options.foo !='number') { throw new error('foo missing.'); }   if (typeof options.bar !='string') { throw new error('bar missing.'); }   if (typeof callback!= 'function') { throw new error('callback missing.'); }   // ... }

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