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How can I merge 2 javascript objects, populating the properties in one if they don't exist in the other?

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太阳男子
太阳男子 2021-02-18 16:47

If I have a javascript object/assoc. array defined like this:

function somefunction(options) {

    var defaults = {
        prop1: \'foo\',
        prop2: \'bar
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5条回答
  • 遥遥无期
    2021-02-18 17:11

    Using Google Closure Library it can be done like that:

    goog.require('goog.object');
function somefunction(options) {
  var defaults = {
    prop1: 'foo',
    prop2: 'bar'
  };
  goog.object.extend(defaults, options);
  // if the property is defined in options it will overwrite value.
}
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  • 死守一世寂寞
    2021-02-18 17:14

    After re-reading the question, I realized you're probably looking for something more like this:

    var a = { 'foo': 'bar', 'baz': 'bat' };
var b = { 'foo': 'quux' };
for (var prop in a) {
    if (prop in b) { continue; }
    b[prop] = a[prop];
}
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  • 遇见更好的自我
    2021-02-18 17:15

    You could look at either jQuery's or Prototypes extend functionality.

    It looks like this: (taken directly from jQuery)

    jQuery.extend = jQuery.fn.extend = function() {
    // copy reference to target object
    var target = arguments[0] || {}, i = 1, length = arguments.length, deep = false, options;

    // Handle a deep copy situation
    if ( typeof target === "boolean" ) {
        deep = target;
        target = arguments[1] || {};
        // skip the boolean and the target
        i = 2;
    }

    // Handle case when target is a string or something (possible in deep copy)
    if ( typeof target !== "object" && !jQuery.isFunction(target) )
        target = {};

    // extend jQuery itself if only one argument is passed
    if ( length == i ) {
        target = this;
        --i;
    }

    for ( ; i < length; i++ )
        // Only deal with non-null/undefined values
        if ( (options = arguments[ i ]) != null )
            // Extend the base object
            for ( var name in options ) {
                var src = target[ name ], copy = options[ name ];

                // Prevent never-ending loop
                if ( target === copy )
                    continue;

                // Recurse if we're merging object values
                if ( deep && copy && typeof copy === "object" && !copy.nodeType )
                    target[ name ] = jQuery.extend( deep, 
                        // Never move original objects, clone them
                        src || ( copy.length != null ? [ ] : { } )
                    , copy );

                // Don't bring in undefined values
                else if ( copy !== undefined )
                    target[ name ] = copy;

            }

    // Return the modified object
    return target;
};
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  • 借酒劲吻你
    2021-02-18 17:26 
    <html>
<head> 
<title>Testing</title>

<script type="text/JavaScript">
// The method is simpler than its demonstration:

function merge(obj1, obj2, force){
    for(var p in obj2){
        if(force || obj1[p]=== undefined) obj1[p]= obj2[p];
    }
    return obj1;
}

// demo:
var merge_demo= function(){
    // set up a to string method, just for the demo
    var restring= function(){
        var s= [];
        for(var p in this){
            s[s.length]= p+': '+this[p];
        }
        return '{ '+s.join(', ')+' }';
    }
    // define two objects
    var O1={
        a: 1, b: 2, c: 3
    }
    var O2={
        a: 10, b: 11, d: 4
    }
    // Begin demo, write the object contents to a string:
    var str= 'Object1='+restring.call(O1)+'\nObject2='+restring.call(O2)+'\n\n';

    //merge the two objects without overwriting values: 
    merge(O1, O2);

    // Update object contents in string:
    str+= 'merge(Object1,Object2)='+restring.call(O1)+'\n\n';

    //merge and replace existing values:
    merge(O1, O2, true);

    // Update and return string: 
    str+= 'merge(Object1,Object2,true)='+restring.call(O1);
    return str;
}
alert(merge_demo());
</script>
</head>

<body>
</body>
</html>
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  • 小蘑菇
    2021-02-18 17:29

    I'm a PrototypeJS holdout. Us Java-types prefer PrototypeJS's OO design over jQuery. Here's how you merge two Object/Hash/Maps with Proto:

    $H(obj1).merge(obj2).toObject()

    The input obj1 and obj2 are unaffected. obj2 map entries have precedence (i.e. obj1 and obj2 both have same key, the value for that key in obj2 will override).

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