reference object name with variable - javascript

Question

I have objects representing the days of the week:

var sunday = {
  time7 : "hello",
  time75 : "get up",
  time8 : "brush your teeth"
};
var monday = {
  time7 : "hello",
  time75 : "get up",
  time8 : "brush your teeth"
};

etc...

I then have a function which checks the day and time, and then updates the webpage:

function schedgie() {
  var now = new Date();
  var day = now.getDay();
  var hour = now.getHours();
  var minute = now.getMinutes();
  var dayRange = ["sunday","monday", "tuesday", "wednesday", "thursday", "friday", "saturday"];
  var today = dayRange[day];
  if ((hour == "7") && (minute >= "0" && minute <= "29")) {
    document.getElementById("max").innerHTML = today.time7; 
  }
  if ((hour == "7") && (minute >= "30" && minute <= "59")) {
    document.getElementById("max").innerHTML = today.time75;
  }
};

The "today" variable however is not referencing the object name as I hoped. Any assistance would be greatly appreciated. Thank you!

dayRange is array. it sould be accessible with indexes like dayRange[0], etc — Md Junaid Alam
– Md Junaid Alam, Commented Apr 12, 2020 at 19:57
You cant do this. Your objects are given labels like sunday, monday, etc that the interpreter understands. When the interpreter looks what you set the label "today" as by way of "var today=dayRange[day];" it doesnt see the label for your objects, it just sees "a string", any string. It treates the "today" as a string with a value and makes no attempt to reference an object that also happens to have the same label as the value of that string. — Stephen Duffy
– Stephen Duffy, Commented Apr 12, 2020 at 20:21

mikado · Accepted Answer · 2020-04-12 19:59:24Z

2

dayRange as you have it defined is simply an array of strings and has nothing to do with the objects you defined for representing the days of the week.

You need to change the definition of dayRange to

dayRange = [sunday, monday, tuesday, wednesday, thursday, friday, saturday];

Notice the missing "s!

answered Apr 12, 2020 at 19:59

mikado

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Comments

Brian Thompson · Accepted Answer · 2020-04-12 19:57:51Z

1

The value you're accessing from the array is just a string, not the object reference. Just because the string value is the same as the object name doesn't have any special effect.

You might be able to get it working as easily as removing the " " around the weekday names so that they are variables instead of strings. But without knowing the full context of the code I can't say for sure

answered Apr 12, 2020 at 19:57

Brian Thompson

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2 Comments

John Lord Over a year ago

he would also have to get rid of the eval() around the reference.

John Lord Over a year ago

whoops. You're right. I was looking at an answer.

Ivan86 · Accepted Answer · 2020-04-12 20:19:30Z

0

You can use eval() for this purpose, but it is a dangerous function to use. You might want to think of a different way to organize your data.

E.g. you could have an object days that has keys sunday, monday, etc. In that case it would be as simple as days[today].time75 to get the value you desire.

eval():

The argument of the eval() function is a string. If the string represents an expression, eval() evaluates the expression. If the argument represents one or more JavaScript statements, eval() evaluates the statements.

Warning: Executing JavaScript from a string is an enormous security risk. It is far too easy for a bad actor to run arbitrary code when you use eval().

more here.

Solution with eval():

Note: I put hour == hour in the if statement just so we can prove that it works (we might be in different time zones).

var sunday = {
  time7 : "hello",
  time75 : "get up",
  time8 : "brush your teeth"
};
var monday = {
  time7 : "hello",
  time75 : "get up",
  time8 : "brush your teeth"
};

function schedgie() {
  var now = new Date();
  var day = now.getDay();
  var hour = now.getHours();
  var minute = now.getMinutes();
  var dayRange = ["sunday","monday", "tuesday", "wednesday", "thursday", "friday", "saturday"];
  var today = dayRange[day];
  if ((hour == hour) && (minute >= "0" && minute <= "29")) {
    document.getElementById("max").innerHTML = eval(today).time7; 
  }
  if ((hour == hour) && (minute >= "30" && minute <= "59")) {
    document.getElementById("max").innerHTML = eval(today).time75;
  }
};

schedgie();

<div id="max"></div>

A better approach, without eval():

var days = {
  "sunday" : {
    "time7" : "hello",
    "time75" : "get up",
    "time8" : "brush your teeth"
  },
  "monday" : {
    "time7" : "hello",
    "time75" : "get up",
    "time8" : "brush your teeth"
  }
};

console.log( days["sunday"].time7 );
console.log( days["monday"].time8 );

edited Apr 12, 2020 at 20:19

answered Apr 12, 2020 at 19:58

Ivan86

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3 Comments

John Lord Over a year ago

people always say eval is a security threat. In reality, it is much easier just to open the console and run the javascript directly. If i have your site loaded, i have full access automatically to all functions and variables you have used. Eval doesn't matter.

Ivan86 Over a year ago

@JohnLord I said it is a security threat too. The problem with eval() is when you are evaluating code or data that comes from outside your application which could be malicious. This data comes from inside so it should be fine. But I also gave a better way of organizing the data which doesn't use eval().

John Lord Over a year ago

yes. using the array directly is a much better solution. All i am saying is it all runs on client side and i don't need an eval() to make it run. Javascript in general should be avoided for anything that has a security risk to it.

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