Why is my required external file being ignored in React Native?

Question

I have two React Native 'scenes', one of which launches puzzles in the other. In launch.js, I retrieve data from a separate data file as follows:

import fileData from './data.js';
//var fileData = require('./data.js'); <= I've had it this way, too; data.js is a module.exports of an array-type object

I pass the data to game.js as follows:

onSelect(passed) {
    var inFileData = fileData; //*** this is just a debugging abstraction so I can see what the values are
    this.props.navigator.replace({
        id: 'game board',
        passProps: {
            title: passed,
            theData: fileData,
            },
   });
}

The data is acquired in game.js,

    constructor(props) {
    super(props);
    this.state = {
        id: 'game board',
        title: this.props.title,
        theData: this.props.theData, //<= here
    };

My problem is that when I do 'stuff' in the game, such as changing a value of a word with

    var data = this.props.theData;
    data[index].word = "test";
    this.setState({theData: data});

when I go back to launch.js (and then back to game.js) these changes persist, even to the extent of having the values in the variable inFileData (the *** comment above) reflect what was changed in the game instead of what's in the data.js file. Also, in game.js I'm unable to hold any sort of copy of the imported data (even with kludgy for-loops to try to duplicate the object) to reset values, all of which leads me to believe I'm missing some key underpinning of React's state model. Can anyone shed some light on where I'm going wrong?

Answer 1

I finally resolved this issue (after spending 2 days on it!) with this cloning function using the deepClone call. The function is described in this excellent article , which I came across on the ancient and much-up-voted StackOverflow question, How do I correctly clone a JavaScript object?

I included the entire "owl" function as deepCopy.js in my React Native project as

var deepCopy = require('./deepCopy.js');

after appending

module.exports = owl;

to the deepCopy.js file, then used it with

var copy = owl.deepCopy(fileData);

and

        this.props.navigator.replace({
        id: 'game board',
        passProps: {
            title: passed,
            theData: copy,
            },

Note that because this isn't a web environment I had to comment out the "HTML DOM Node" section of the owl function as it made references to "document" which React Native didn't appreciate.

I guess the issue here was the depth of the array that was being cloned, and references at deeper levels still being retained. Seems like a more native solution must exist, but at least this works...I'll wait to see if anyone has further input before marking this as answered.

Edit: I'm going to include the code in case it gets taken down:

/* This file is part of OWL JavaScript Utilities.

OWL JavaScript Utilities is free software: you can redistribute it and/or 
modify it under the terms of the GNU Lesser General Public License
as published by the Free Software Foundation, either version 3 of
the License, or (at your option) any later version.

OWL JavaScript Utilities is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public 
License along with OWL JavaScript Utilities.  If not, see 
<http://www.gnu.org/licenses/>.
*/

owl = (function() {
// clone objects, skip other types.
function clone(target) {
    if ( typeof target == 'object' ) {
        Clone.prototype = target;
        return new Clone();
    } else {
        return target;
    }
}


// Shallow Copy 
function copy(target) {
    if (typeof target !== 'object' ) {
        return target;  // non-object have value sematics, so target is already a copy.
    } else {
        var value = target.valueOf();
        if (target != value) { 
            // the object is a standard object wrapper for a native type, say String.
            // we can make a copy by instantiating a new object around the value.
            return new target.constructor(value);
        } else {
            // ok, we have a normal object. If possible, we'll clone the original's prototype 
            // (not the original) to get an empty object with the same prototype chain as
            // the original.  If just copy the instance properties.  Otherwise, we have to 
            // copy the whole thing, property-by-property.
            if ( target instanceof target.constructor && target.constructor !== Object ) { 
                var c = clone(target.constructor.prototype);

                // give the copy all the instance properties of target.  It has the same
                // prototype as target, so inherited properties are already there.
                for ( var property in target) { 
                    if (target.hasOwnProperty(property)) {
                        c[property] = target[property];
                    } 
                }
            } else {
                var c = {};
                for ( var property in target ) c[property] = target[property];
            }

            return c;
        }
    }
}

// Deep Copy
var deepCopiers = [];

function DeepCopier(config) {
    for ( var key in config ) this[key] = config[key];
}
DeepCopier.prototype = {
    constructor: DeepCopier,

    // determines if this DeepCopier can handle the given object.
    canCopy: function(source) { return false; },

    // starts the deep copying process by creating the copy object.  You
    // can initialize any properties you want, but you can't call recursively
    // into the DeeopCopyAlgorithm.
    create: function(source) { },

    // Completes the deep copy of the source object by populating any properties
    // that need to be recursively deep copied.  You can do this by using the
    // provided deepCopyAlgorithm instance's deepCopy() method.  This will handle
    // cyclic references for objects already deepCopied, including the source object
    // itself.  The "result" passed in is the object returned from create().
    populate: function(deepCopyAlgorithm, source, result) {}
};

function DeepCopyAlgorithm() {
    // copiedObjects keeps track of objects already copied by this
    // deepCopy operation, so we can correctly handle cyclic references.
    this.copiedObjects = [];
    thisPass = this;
    this.recursiveDeepCopy = function(source) {
        return thisPass.deepCopy(source);
    }
    this.depth = 0;
}
DeepCopyAlgorithm.prototype = {
    constructor: DeepCopyAlgorithm,

    maxDepth: 256,

    // add an object to the cache.  No attempt is made to filter duplicates;
    // we always check getCachedResult() before calling it.
    cacheResult: function(source, result) {
        this.copiedObjects.push([source, result]);
    },

    // Returns the cached copy of a given object, or undefined if it's an
    // object we haven't seen before.
    getCachedResult: function(source) {
        var copiedObjects = this.copiedObjects;
        var length = copiedObjects.length;
        for ( var i=0; i<length; i++ ) {
            if ( copiedObjects[i][0] === source ) {
                return copiedObjects[i][1];
            }
        }
        return undefined;
    },

    // deepCopy handles the simple cases itself: non-objects and object's we've seen before.
    // For complex cases, it first identifies an appropriate DeepCopier, then calls
    // applyDeepCopier() to delegate the details of copying the object to that DeepCopier.
    deepCopy: function(source) {
        // null is a special case: it's the only value of type 'object' without properties.
        if ( source === null ) return null;

        // All non-objects use value semantics and don't need explict copying.
        if ( typeof source !== 'object' ) return source;

        var cachedResult = this.getCachedResult(source);

        // we've already seen this object during this deep copy operation
        // so can immediately return the result.  This preserves the cyclic
        // reference structure and protects us from infinite recursion.
        if ( cachedResult ) return cachedResult;

        // objects may need special handling depending on their class.  There is
        // a class of handlers call "DeepCopiers"  that know how to copy certain
        // objects.  There is also a final, generic deep copier that can handle any object.
        for ( var i=0; i<deepCopiers.length; i++ ) {
            var deepCopier = deepCopiers[i];
            if ( deepCopier.canCopy(source) ) {
                return this.applyDeepCopier(deepCopier, source);
            }
        }
        // the generic copier can handle anything, so we should never reach this line.
        throw new Error("no DeepCopier is able to copy " + source);
    },

    // once we've identified which DeepCopier to use, we need to call it in a very
    // particular order: create, cache, populate.  This is the key to detecting cycles.
    // We also keep track of recursion depth when calling the potentially recursive
    // populate(): this is a fail-fast to prevent an infinite loop from consuming all
    // available memory and crashing or slowing down the browser.
    applyDeepCopier: function(deepCopier, source) {
        // Start by creating a stub object that represents the copy.
        var result = deepCopier.create(source);

        // we now know the deep copy of source should always be result, so if we encounter
        // source again during this deep copy we can immediately use result instead of
        // descending into it recursively.  
        this.cacheResult(source, result);

        // only DeepCopier::populate() can recursively deep copy.  So, to keep track
        // of recursion depth, we increment this shared counter before calling it,
        // and decrement it afterwards.
        this.depth++;
        if ( this.depth > this.maxDepth ) {
            throw new Error("Exceeded max recursion depth in deep copy.");
        }

        // It's now safe to let the deepCopier recursively deep copy its properties.
        deepCopier.populate(this.recursiveDeepCopy, source, result);

        this.depth--;

        return result;
    }
};

// entry point for deep copy.
//   source is the object to be deep copied.
//   maxDepth is an optional recursion limit. Defaults to 256.
function deepCopy(source, maxDepth) {
    var deepCopyAlgorithm = new DeepCopyAlgorithm();
    if ( maxDepth ) deepCopyAlgorithm.maxDepth = maxDepth;
    return deepCopyAlgorithm.deepCopy(source);
}

// publicly expose the DeepCopier class.
deepCopy.DeepCopier = DeepCopier;

// publicly expose the list of deepCopiers.
deepCopy.deepCopiers = deepCopiers;

// make deepCopy() extensible by allowing others to 
// register their own custom DeepCopiers.
deepCopy.register = function(deepCopier) {
    if ( !(deepCopier instanceof DeepCopier) ) {
        deepCopier = new DeepCopier(deepCopier);
    }
    deepCopiers.unshift(deepCopier);
}

// Generic Object copier
// the ultimate fallback DeepCopier, which tries to handle the generic case.  This
// should work for base Objects and many user-defined classes.
deepCopy.register({
    canCopy: function(source) { return true; },

    create: function(source) {
        if ( source instanceof source.constructor ) {
            return clone(source.constructor.prototype);
        } else {
            return {};
        }
    },

    populate: function(deepCopy, source, result) {
        for ( var key in source ) {
            if ( source.hasOwnProperty(key) ) {
                result[key] = deepCopy(source[key]);
            }
        }
        return result;
    }
});

// Array copier
deepCopy.register({
    canCopy: function(source) {
        return ( source instanceof Array );
    },

    create: function(source) {
        return new source.constructor();
    },

    populate: function(deepCopy, source, result) {
        for ( var i=0; i<source.length; i++) {
            result.push( deepCopy(source[i]) );
        }
        return result;
    }
});

// Date copier
deepCopy.register({
    canCopy: function(source) {
        return ( source instanceof Date );
    },

    create: function(source) {
        return new Date(source);
    }
});

// HTML DOM Node

// utility function to detect Nodes.  In particular, we're looking
// for the cloneNode method.  The global document is also defined to
// be a Node, but is a special case in many ways.
function isNode(source) {
    if ( window.Node ) {
        return source instanceof Node;
    } else {
        // the document is a special Node and doesn't have many of
        // the common properties so we use an identity check instead.
        if ( source === document ) return true;
        return (
            typeof source.nodeType === 'number' &&
            source.attributes &&
            source.childNodes &&
            source.cloneNode
        );
    }
}

// Node copier
deepCopy.register({
    canCopy: function(source) { return isNode(source); },

    create: function(source) {
        // there can only be one (document).
        if ( source === document ) return document;

        // start with a shallow copy.  We'll handle the deep copy of
        // its children ourselves.
        return source.cloneNode(false);
    },

    populate: function(deepCopy, source, result) {
        // we're not copying the global document, so don't have to populate it either.
        if ( source === document ) return document;

        // if this Node has children, deep copy them one-by-one.
        if ( source.childNodes && source.childNodes.length ) {
            for ( var i=0; i<source.childNodes.length; i++ ) {
                var childCopy = deepCopy(source.childNodes[i]);
                result.appendChild(childCopy);
            }
        }
    }
});

return {
    DeepCopyAlgorithm: DeepCopyAlgorithm,
    copy: copy,
    clone: clone,
    deepCopy: deepCopy
};
})();

module.exports = owl;