應用場景

最近在搞微信小程式，這裡面直接引入jquery的話會報錯，但是專案用到了jq的extend方法，在這裡抽離出這個函式，可以引入直接應用

抽離$.extend原始碼

var class2type = {};
var toString = class2type.toString;
var hasOwn = class2type.hasOwnProperty;
var support = {};

function extend() {
    var src, copyIsArray, copy, name, options, clone,
        target = arguments
 
[0] || {},
        i = 1,
        length = arguments.length,
        deep = false;

    // Handle a deep copy situation
    if ( typeof target === "boolean" ) {
        deep = target;

        // skip the boolean and the target
        target = arguments[ i ] || {};
        i++;
    }

    // Handle case when target is a string or something (possible in deep copy)
 

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

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

    for ( ; i < length; i++ ) {
        // Only deal with non-null/undefined values
 

        if ( (options = arguments[ i ]) != null ) {
            // Extend the base object
            for ( name in options ) {
                src = target[ name ];
                copy = options[ name ];

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

                // Recurse if we're merging plain objects or arrays
                if ( deep && copy && ( isPlainObject(copy) || (copyIsArray = isArray(copy)) ) ) {
                    if ( copyIsArray ) {
                        copyIsArray = false;
                        clone = src && isArray(src) ? src : [];

                    } else {
                        clone = src && isPlainObject(src) ? src : {};
                    }

                    // Never move original objects, clone them
                    target[ name ] = extend( deep, clone, copy );

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

    // Return the modified object
    return target;
}

// isPlainObject isFunction isArray isWindow type

function isPlainObject( obj ) {
    var key;

    // Must be an Object.
    // Because of IE, we also have to check the presence of the constructor property.
    // Make sure that DOM nodes and window objects don't pass through, as well
    if ( !obj || type(obj) !== "object" || obj.nodeType || isWindow( obj ) ) {
        return false;
    }

    try {
        // Not own constructor property must be Object
        if ( obj.constructor &&
            !hasOwn.call(obj, "constructor") &&
            !hasOwn.call(obj.constructor.prototype, "isPrototypeOf") ) {
            return false;
        }
    } catch ( e ) {
        // IE8,9 Will throw exceptions on certain host objects #9897
        return false;
    }

    // Support: IE<9
    // Handle iteration over inherited properties before own properties.
    if ( support.ownLast ) {
        for ( key in obj ) {
            return hasOwn.call( obj, key );
        }
    }

    // Own properties are enumerated firstly, so to speed up,
    // if last one is own, then all properties are own.
    for ( key in obj ) {}

    return key === undefined || hasOwn.call( obj, key );
}


function isFunction( obj ) {
    return type(obj) === "function";
}

function isArray( obj ) {
    return type(obj) === "array";
}

function isWindow( obj ) {
    /* jshint eqeqeq: false */
    return obj != null && obj == obj.window;
}

function type( obj ) {
    if ( obj == null ) {
        return obj + "";
    }
    return typeof obj === "object" || typeof obj === "function" ?
        class2type[ toString.call(obj) ] || "object" :
        typeof obj;
}

應用示例

// 淺拷貝
var result1 = extend({},  
    { name: "John", location: {city: "Boston",county:"USA"} },  
    { last: "Resig", location: {state: "MA",county:"China"} } ); 
console.log(result1);

// 深拷貝
var result2 = extend(true, {},  
    { name: "John", location: {city: "Boston",county:"USA"} },  
    { last: "Resig", location: {state: "MA",county:"China"} } ); 
console.log(result2);

封裝簡單的深拷貝程式碼

function deepCopy(obj) {
  if (typeof obj != 'object') return obj
  // 判斷陣列還是物件，同時開闢一個新的地址空間(注意用instanceOf或constructor在iframe中會失效)
  let copyObj = Array.isArray(obj) ? [] : {}
  for (let key in obj) {
    // 遞迴呼叫
    copyObj[key] = deepClone(obj[key])
  }
  return copyObj
}

應用示例

// 深拷貝
let result2 = deepCopy({ name: "John", location: { city: "Boston", county: "USA" } })