Question

我正在寻找关于这段代码的澄清：

// Taken from alert create class call for clarification
_createClass(Alert, null, [{
    key: 'VERSION',
    get: function get() {
        return VERSION;
    }
}]);

return Alert;

// Taken from BS boilerplate
var _createClass = function () {
    function defineProperties(target, props) {
        for (var i = 0; i < props.length; i++) {
            var descriptor = props[i];
            descriptor.enumerable = descriptor.enumerable || false;
            descriptor.configurable = true;

            if ("value" in descriptor) {
                descriptor.writable = true;
            }

            Object.defineProperty(target, descriptor.key, descriptor);
        }
    }

    return function (Constructor, protoProps, staticProps) {
        if (protoProps) {
            defineProperties(Constructor.prototype, protoProps);
        }

        if (staticProps) {
            defineProperties(Constructor, staticProps);
        }

        return Constructor; 
    };
}();

我不确定参数Alert，null和数组对象在不接受任何参数时如何传递给createClass。我假设他们以某种方式得到了其他嵌套函数，但我不确定如何。

Answer 1

{ "phoneNumbers": [ { "type": "home", "number": "212 555-1234" }, { "type": "office", "number": "646 555-4567" }, { "type": "mobile", "number": "123 456-7890" } ] }被分配了该函数的结果。这是因为该函数是一个立即调用的函数表达式（IIFE） - 因此它的末尾是_createClass。

所以()真的是：

_createClass

Answer 2

我立即删除了调用的函数表达式（IIFE）包装器

defineProperties

为了清晰起见，

并将defineProperties功能移到了外面。

但我需要说IIFE包装器首先是在IIFE之外没有泄漏const defineProperties = (/*Alert*/target, /*[{...}]*/props) => { props.forEach(function(/*{...}*/descriptor) { // assigning false because we don't have it specified // in props object descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; // we don't have value either, so - skipping... if ("value" in descriptor) descriptor.writable = true; // assigning VERSION prop with earlier decorated descriptor {...} Object.defineProperty(target, descriptor.key, descriptor); // Now our Alert function has VERSION key, which returns 'VERSION' with its getter function }); } const _createClass = (/*Alert*/Constructor, /*null*/protoProps, /*[{...}]*/staticProps) => { if (protoProps) { //not going here obviously because protoProps null defineProperties(Constructor.prototype, protoProps); } if (staticProps) { // going here because [{...}] defineProperties(Constructor, staticProps); } // returning class with decorated static property VERSION return Constructor; }; _createClass( Alert, //Constructor null, //protoProps [{ //staticProps key: 'VERSION', get: function get() { return VERSION; } }] );功能。因此，在大多数情况下，基本上需要IIFE来包含一次创建的所有私有变量。

除此之外，请看一下这个调试风格的逐步重构版本。

import tkinter.font
from tkinter import *

root = Tk()
# Get a font object
font_obj = tkinter.font.Font()
canvas = Canvas(root)
canvas.grid()
string_list = []
string_list.append('the text that is too wide for the canvas and I need to know that it is')
string_list.append('this text will fit')

# Iterate through the strings, getting the number of pixels it takes.
# Note that this can be configured larger or smaller based on need.
can_width = int(canvas['width'])
i = 0
for s in string_list:
    str_pixels = font_obj.measure(s, canvas)
    # Compare the width of the canvas to the number of str_pixels
    if str_pixels <= can_width:
        y = (i + 1) * 20
        canvas.create_text(10,y,anchor='nw',text=s,font='TkDefault')
        i += 1
    else:
        # Print a warning, ignore, whatever when the string is too long.
        print("'" + s + "'", "is too long to display in canvas")

root.mainloop()

Bootstrap中的嵌套函数

2 个答案: