README_v.3.x.x.md

Walk (@peter.naydenov/walk) ( Version 3.x.x )

• Documentation for old v.2.x.x
• Migration guides

Creates an immutable copies of javascript data structures(objects, arrays or mixed). Executes callback functions on every object property(object-callback) and every primitive property(key-callback). Callbacks can modify result object during the walk process. Mask, filter or substitute values during the copy process.

const result = walk ({
                            data             // (required) Any JS data structure;
                          , objectCallback   // (optional) Function executed on each object property;
                          , keyCallback      // (optional) Function executed on each primitive property;
                    })
// Result will become a exact deep copy of "data" 
// - if callbacks are not defined
// - if callbacks are resolved with "value" without modification

keyCallback

function "keyCallback" of the walk could be used also as a deep 'forEach' method no matter of the type of the object(object or array).

function keyCallbackFn ({value,key,breadcrumbs}) {
    // value: value for the property
    // key:  key of the property
    // breadcrumbs: location of the property
    // Callback should return the value of the property. If function returns 'null' or 'undefined', property will be ignored.
  }

let result = walk ({ data, keyCallback: keyCallbackFn });  // It's the short way to provide only key-callback. Callback functions are optional.
// let result = walk ({ data, keyCallback, objectCallback });  // If both callbacks are available

objectCallback

Optional callback function that is started on each object property. Function should return object or will be ignored in copy process.

function objectCallbackFn ({ value, key, breadcrumbs }) {
      // value: each object during the walk
      // key: key of the object
      // breadcrumbs: location of the object
      // object callback should return an object.
}

let result = walk ({ data, keyCallback:keyCallbackFn, objectCallback : objectCallbackFn })

IMPORTANT: Object-callbacks are executed always before key-callbacks. If we have both callbacks, then key-callbacks will be executed on the result of object-callback.

Skip key-callbacks by not defining them:

 let result = walk ({ data, objectCallback: objectCallbackFn })   // ignore keyCallback

Installation

Install for node.js projects by writing in your terminal:

npm install @peter.naydenov/walk

Once it has been installed, it can be used by writing this line of JavaScript:

let walk = require ( '@peter.naydenov/walk' )

or

import walk from '@peter.naydenov/walk'

Installation for browsers: Get the file "dist/walk.min.js" and put it inside the project. Request the file from HTML page. Global variable 'walk' is available for use.

Versions of walk after v.3.1.x are buided as ES module, so don't forget to add type="module".

    Note:
    Library is using 'generator functions'. If support for old browsers 
    is required, add a polyfill for 'generators'.

How to use it

Deep copy

let myCopy = walk ({ data:x })   // where x is some javascript data structure

Deep 'forEach'

let x = {
          ls    : [ 1,2,3 ]
        , name  : 'Peter'
        , props : {
                      eyeColor: 'blue'
                    , age     : 47
                    , height  : 176
                    , sizes : [12,33,12,21]
                }
    };

walk ({ data:x, keyCallback : ({value,key, breadcrumbs}) => {
                  console.log (`${key} ----> ${value}`)   // Show each each primitive couples key->value
                  console.log ( `Property location >> ${breadcrumbs}`)
                  // example for breadcrumbs: 'age' will looks like this : 'root/props/age'
              }
    })

Ignore a key

let x = {
          ls    : [ 1,2,3 ]
        , name  : 'Peter'
        , props : {
                      eyeColor: 'blue'
                    , age     : 47
                    , height  : 176
                    , sizes : [12,33,12,21]
                }
    };
let result = walk ({ data:x, keyCallback : ({value,key}) => {
                        if ( key === 'name' )   return null
                        return value
                })
// result will copy all properties from x without the property 'name'.
// result.name === undefined

Mask values

let x = {
          ls    : [ 1,2,3 ]
        , name  : 'Peter'
        , props : {
                      eyeColor: 'blue'
                    , age     : 47
                    , height  : 176
                    , sizes : [12,33,12,21]
                }
    };
let result = walk ({ data:x, keyCallback : () => 'xxx' })
// 'result' will have the same structure as 'x' but all values are 'xxx'
// {
//      ls    : [ 'xxx','xxx','xxx' ]
//    , name  : 'xxx'
//    , props : {
//                  eyeColor: 'xxx'
//                , age     : 'xxx'
//                , height  : 'xxx'
//                , sizes : ['xxx','xxx','xxx','xxx']
//             }
//   } 

Change object on condition

let x = {
          ls    : [ 1,2,3 ]
        , name  : 'Peter'
        , props : {
                      eyeColor: 'blue'
                    , age     : 48
                    , height  : 176
                    , sizes : [12,33,12,21]
                }
    };

function objectCallback ({ value:obj, key, breadcrumbs }) {
    const {age, height} = obj;
    if ( age && age > 30 ) {
            return { age, height }
        }
    return obj
}

let result = walk ({ data:x, objectCallback })
// 'result.props' will have only 'age' and 'height' properties.
// {
//      ls    : [ 1,2,3 ]
//    , name  : 'Peter'
//    , props : {
//                  age     : 48
//                , height  : 176
//             }
//   } 

Limitations

• walk keyCallback can return only primitives;
• walk can not execute another walk from inside of the callbacks;
• It's not recomended to use any async operations in the callbacks. Could compromise the result without any warning;

These limitations are covered in a bit larger library - walk-async. Interface is very simular but result is coming as a promise and callbacks should be resolved or rejected.

Links

• Release history

Credits

'@peter.naydenov/walk' was created and supported by Peter Naydenov.

License

'@peter.naydenov/walk' is released under the MIT License.