JavaScript: merge two objects

gistfile1.js

function merge(target, source) {
        
    /* Merges two (or more) objects,
       giving the last one precedence */
    
    if ( typeof target !== 'object' ) {
        target = {};
    }
    
    for (var property in source) {
        
        if ( source.hasOwnProperty(property) ) {
            
            var sourceProperty = source[ property ];
            
            if ( typeof sourceProperty === 'object' ) {
                target[ property ] = util.merge( target[ property ], sourceProperty );
                continue;
            }
            
            target[ property ] = sourceProperty;
            
        }
        
    }
    
    for (var a = 2, l = arguments.length; a < l; a++) {
        merge(target, arguments[a]);
    }
    
    return target;
};

function merge(target: { [x: string]: {} }, source: { [x: string]: {} }) {

    /* Merges two (or more) objects,
       giving the last one precedence */

    if (typeof target !== "object") {
        target = {};
    }

    for (const property in source) {

        if (source.hasOwnProperty(property)) {

            const sourceProperty = source[property];

            if (typeof sourceProperty === "object" &&
                // tslint:disable-next-line:no-null-keyword
                sourceProperty !== null &&
                sourceProperty.constructor !== Array
            ) {
                target[property] = merge(target[property], sourceProperty);
                continue;
            }

            target[property] = sourceProperty;

        }

    }

    // tslint:disable-next-line:one-variable-per-declaration
    for (let a = 2, l = arguments.length; a < l; a++) {
        merge(target, arguments[a]);
    }

    return target;
}

// {} Ensures that there cannot be only 1 argument
merge({}, {}, ...sourceFixture);