underscore.comparison.islike.js.md

comparison.islike

This is a function to check things, and particularly complex objects, fit a certain pattern. It is useful when you want to check that an argument you have received has the properties you expect.

Signature: _.islike(object:Any, pattern:Any)

Returns true if the object is like the pattern. false otherwise.

_.islike(
  {name: "James", age: 10, hobbies: ["football", "computer games", "baking"]},
  {name: "", age: 0, hobbies: [""]}
)

Basic types

To specify that a value should be a string you can put an empty string in the pattern "". For a number use 0 and for an array use an empty array [].

• "" - stands for a string
• 0 - stands for a number
• false - stands for a boolean
• [] - stands for an array
• Function - stands for a function

If you specify a type in the pattern then the value will be tested using instanceof. If you want to verify a function value (for instance a callback) you need to pass the Function type, since a normal function() {} is indistinguishable from type in Javascript. A more complex example using these follows:

_.islike(myArgument, {
    title: "", count: "", owner: OwnerModel, success: Function, error: Function
});

Array types

An array value can also be type checked by passing an array of types in the pattern. For example

• _.islike([ 1, 2, 3, "hello" ], [ 0 ]) - returns false
• _.islike([ 1, 2, 3, "hello", function() {} ], [ 0, "" ]) - returns false
• _.islike([ 1, 2, 3, "hello" ], [ 0, "" ]} - returns true
• _.islike([ 1, 2, 3, "hello", function() {} ], [ 0, "", Function ]} - returns true

[""] allows an array of only strings and ["",0] allows strings and numbers. This check is done using typeof so objects and arrays will fall into the same category.

Complex nested objects

Nested objects are recursively checked, so you just need to nest your pattern.

This is a very complex example, probably more complex than _.islike is suited for, but is shows the nesting. In the example the object has a process property with two callback functuons and an array of numbers. It also has an author property which has another nested location property.

_.islike(myComplexArgument,
    title: "", age: 0, popularity: 0, available: false,
    process: {
        success: Function, error: Function, values: [0]
    },
    author: {
        name: "", location: { country: "", city: "", postcode: "" }
    }
});