Question

我在javascript中创建一个数组，在其中插入一个元素，然后使用import sys from PyQt4 import QtCore, QtGui class Thread(QtCore.QThread): dataReceived = QtCore.pyqtSignal(str) def run(self): # subprocess stuff goes here for step in range(6): self.sleep(1) self.dataReceived.emit('data received: %d' % step) class Window(QtGui.QMainWindow): def __init__(self): super(Window, self).__init__() self.button = QtGui.QPushButton('Start') self.button.clicked.connect(self.handleButton) self.setCentralWidget(self.button) self.thread = Thread(self) self.thread.dataReceived.connect(self.statusBar().showMessage) def handleButton(self): if not self.thread.isRunning(): self.statusBar().showMessage('starting...') self.thread.start() def closeEvent(self, event): self.thread.wait() if __name__ == "__main__": app = QtGui.QApplication(sys.argv) window = Window() window.resize(200, 60) window.show() sys.exit(app.exec_())检查它的存在。它返回true。但是当我使用includes将数组转换为字符串然后使用JSON.stringify转换回数组然后测试相同时，它返回false。

令我感到困惑。

JSON.parse

这是一个jsbin。

Answer 1

当您运行json.parse时，您将返回一个新对象。使用includes时，对象按身份而不是值进行比较，这就是返回false的原因。如果您愿意，可以修改includes原型（虽然我不建议这样做）进行更深层次的对象比较

Array.prototype.includes = function(searchElement /*, fromIndex*/) {
    'use strict';
    if (this == null) {
      throw new TypeError('Array.prototype.includes called on null or undefined');
    }

    var O = Object(this);
    var len = parseInt(O.length, 10) || 0;
    if (len === 0) {
      return false;
    }
    var n = parseInt(arguments[1], 10) || 0;
    var k;
    if (n >= 0) {
      k = n;
    } else {
      k = len + n;
      if (k < 0) {k = 0;}
    }
    var currentElement;
    while (k < len) {
       currentElement = O[k];
       if (JSON.stringify(searchElement) === JSON.stringify(currentElement) || searchElement === currentElement ||
         (searchElement !== searchElement && currentElement !== currentElement)) { // NaN !== NaN
        return true;
      }
      k++;
    }
    return false;
};

请注意，此代码基于Array.prototype.includes polyfill。

Answer 2

因为winhowes州包括按身份检查而不是价值。

你可以试试这个：

if (!Array.prototype.includesCallback) {
    Array.prototype.includesCallback = function(predicate) {
        'use strict';
        if (this == null) {
            throw new TypeError('Array.prototype.includeCallback called on null or undefined');
        }
        if (typeof predicate !== 'function') {
            throw new TypeError('predicate must be a function');
        }
            var list = Object(this);
            var length = list.length >>> 0;
            var thisArg = arguments[1];
            var value;

            for (var i = 0; i < length; i++) {
            value = list[i];
            if (predicate.call(thisArg, value, i, list)) {
                return true;
            }
        }
        return undefined;
    };
}

可以让你利用一个函数来执行comparasin

later.includesCallback (
    function(item) {
        return item.id === test_object.id;
    }
);

Answer 3

＆＃13;

Array.prototype.includesEquivalent = function (obj) {
	for (var o in this) {
	  for (var p in this[o]) {
		if (this[o][p] !== obj[p]) {
		  return false;
		}
	  }
	}
	
	return true;
}

var test_object = {'id': 1, 'name': 'Test'};
var initial = [];

initial.push(test_object);
console.log(initial.includes(test_object));

var later = JSON.stringify(initial);
later = JSON.parse(later);

console.log(later.includesEquivalent(test_object));

＆＃13;

Javascript数组包括在JSON.parse之后返回false

3 个答案: