JavaScript：console.log（）给出的结果与alert（）不同 [英] JavaScript: console.log() gives different results than alert()

问题描述

console.log（）是否应该在JavaScript中调用变量时打印出变量的值？这是我的假设，但当我在Firefox（使用Firebug）或谷歌Chrome（并使用内置的开发工具）中运行下面的代码时，我似乎得到了数组的最终值，而不是当时的数组。如果我使用alert（）语句，它们会打印出我期望的内容 - 调用alert（）语句时数组的值。

Is console.log() supposed to print out the value of a variable at the time it's called in your JavaScript? That was my assumption but when I run the code below in either Firefox (using Firebug) or Google Chrome (and use the built-in dev tools), I seem to get the "final" value of an array rather than the value of the array at that time. If I use alert() statements they print out what I would expect - the value of an array at the time the alert() statement is called.

var params = new Array();
var tmp = new Array('apple', 'banana', 'cat');

for (var i=0; i < tmp.length; i++) {
    params[tmp[i]] = [];
}

console.log(params);
/*
SHOWS IN CONSOLE:

- []
+ apple             ["jan", "feb", "mar", "apr"]
+ banana            ["jan", "feb", "mar", "apr"]
+ apple             ["jan", "feb", "mar", "apr"]
*/

alert( print_arr(params) );
/* 
ALERT BOX TEXT:

[apple]:
[banana]:
[cat]:
*/

console.log('===========================================');

var tmp2 = new Array('jan', 'feb', 'mar', 'apr');
for (var i=0; i < tmp.length; i++) {
    for (var j=0; j < tmp2.length; j++) {
        params[tmp[i]].push(tmp2[j]);
    }
}           

console.log(params);
/*
SHOWS IN CONSOLE:

- []
+ apple             ["jan", "feb", "mar", "apr"]
+ banana            ["jan", "feb", "mar", "apr"]
+ apple             ["jan", "feb", "mar", "apr"]
*/

alert( print_arr(params) );
/* 
ALERT BOX TEXT:

[apple]:jan,feb,mar,apr
[banana]:jan,feb,mar,apr
[cat]:jan,feb,mar,apr
*/

function print_arr(arr) {
    var str = '';
    for (var k in arr) {
        str += '[' + k + ']:' + arr[k].toString() + "\n";

    }

    return str;
}

推荐答案

正如我在评论中所说 console.log（obj）不记录字符串表示，它记录对内存中实际javascript对象的引用。因此，对对象所做的任何更改都将反映在记录的实例中。

As I said in the comments console.log(obj) does not log a string representation, it logs a reference to the actual javascript object in the memory. So any changes made to the object will get reflected in the logged instance.

如果要跟踪所做的渐进式更改，请将对象转换为字符串并打印到喜欢 console.log（JSON.stringify（params））。

If you want to trace the progressive changes made, then convert the object to a string and print to like console.log(JSON.stringify(params)).

此外你还没有使用 params 作为数组，您将其用作地图。所以将 params 更改为对象 var params = {}

Also you are not using params as an array, you are using it as an map. so change params to an object var params = {}

将 params 更改为对象并使用 JSON.stringify 进行记录

Change params to an object and use JSON.stringify to log it

var params = {};
var tmp = new Array('apple', 'banana', 'cat');

for (var i=0; i < tmp.length; i++) {
    params[tmp[i]] = [];
}

console.log(JSON.stringify(params));
/*
SHOWS IN CONSOLE:

- []
+ apple             ["jan", "feb", "mar", "apr"]
+ banana            ["jan", "feb", "mar", "apr"]
+ apple             ["jan", "feb", "mar", "apr"]
*/

alert( print_arr(params) );
/* 
ALERT BOX TEXT:

[apple]:
[banana]:
[cat]:
*/

console.log('===========================================');

var tmp2 = new Array('jan', 'feb', 'mar', 'apr');
for (var i=0; i < tmp.length; i++) {
    for (var j=0; j < tmp2.length; j++) {
        params[tmp[i]].push(tmp2[j]);
    }
}           

console.log(JSON.stringify(params));
/*
SHOWS IN CONSOLE:

- []
+ apple             ["jan", "feb", "mar", "apr"]
+ banana            ["jan", "feb", "mar", "apr"]
+ apple             ["jan", "feb", "mar", "apr"]
*/

alert( print_arr(params) );
/* 
ALERT BOX TEXT:

[apple]:jan,feb,mar,apr
[banana]:jan,feb,mar,apr
[cat]:jan,feb,mar,apr
*/

function print_arr(arr) {
    var str = '';
    for (var k in arr) {
        str += '[' + k + ']:' + arr[k].toString() + "\n";

    }

    return str;
}

演示：小提琴

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