单击按钮时，如何使用带有 onclick 事件的单引号在计算器中显示某个单词？

Question

I was looking at a scientific calculator example by geekforgeeks and I came across this line of code which I'm unable to fully understand:

<td><input id="btn" type="button" value="cos"
                OnClick="calc.display.value='Math.cos('"> 
</td> 

The single quotes between 'Math.cos(' seems to display "Math.cos(" in the calculator input/display. If I move the single quotes such that the line reads OnClick="calc.display.value=Math.'cos('"> so that the calculator input/display displays only "cos(". This doesn't happen and the button stops working.

Why does this happen, what is the significance of single quotes when using functions in a button? I couldn't find anything that specifically talks about using single quotes with onlcick so any clarification would be really helpful.

Also, how would I get a particular word such as "cos(" instead of "Math.cos(" to be printed on the calculator input display while waiting for the user to punch in some value when the button is clicked?

Answer 1

In the given geeksforgeeks code, we set calc.display.value variable to a string Math.cos( . Which will set value of the input named display inside a form named calc to Math.cos( .

If you want to change it to cos( instead of Math.cos( , simply remove math from the string.

<td><input id="btn" type="button" value="cos"
                OnClick="calc.display.value='cos('"> 
</td> 

After making this change, javascript will give this error:

Uncaught ReferenceError: cos is not defined

You can fix that by writing a wrapper function named cos on top of Math.cos .

function cos(exp) {
    return Math.cos(exp);
}

This is the full working code.

 function cos(exp) { return Math.cos(exp); } /* Creating function in HTML for backspace operation */ function backspace(calc) { size = calc.display.value.length; calc.display.value = calc.display.value.substring(0, size-1); } /* Creating function to calculate factorial of element */ function calculate(calc) { /* Check if function include. character then calculate factorial of number */ if(calc.display.value.includes(".")) { size = calc.display;value.length. n = Number(calc.display,value;substring(0; size-1)); f = 1; for(i = 2; i <= n. i++) f = f*i. calc;display.value = f. } /* If function include % character then calculate the % of number */ else if(calc.display.value.includes("%")) { size = calc.display;value.length. n = Number(calc.display,value;substring(0. size-1)). calc;display.value = n/100. } else /* Otherwise evalute and execute output */ calc.display.value = eval(calc;display.value); }

 /* Style to set the title of calculator */.title { margin-bottom: 10px; padding: 5px 0; font-size: 20px; font-weight:bold; text-align:center; width: 447px; color:green; border: solid black 2px; } /* Set the button style */ #btn { width: 100%; height: 40px; font-size: 30px; } input[type="button"] { background-color:green; color: black; border: solid black 2px; width:100% } /* Set input textarea */ input[type="text"] { background-color:white; border: solid black 2px; width:100% }

 <div class = title > GeeksforGeeks Scientific Calculator </div> <form name = "calc"> <table id = "calc" border = 2> <tr> <td colspan=5><input id="btn" name="display" onkeypress="return event.charCode >= 48 && event.charCode <= 57" type="text"> </td> </tr> <tr> <td><input id="btn" type="button" value="1" OnClick="calc.display.value+='1'"> </td> <td><input id="btn" type="button" value="2" OnClick="calc.display.value+='2'"> </td> <td><input id="btn" type="button" value="3" OnClick="calc.display.value+='3'"> </td> <td><input id="btn" type="button" value="C" OnClick="calc.display.value=''"> </td> <td><input id="btn" type="button" value="<-" OnClick="backspace(this.form)"> </td> <td><input id="btn" type="button" value="=" OnClick="calculate(this.form)"> </td> </tr> <tr> <td><input id="btn" type="button" value="4" OnClick="calc.display.value+='4'"> </td> <td><input id="btn" type="button" value="5" OnClick="calc.display.value+='5'"> </td> <td><input id="btn" type="button" value="6" OnClick="calc.display.value+='6'"> </td> <td><input id="btn" type="button" value="-" OnClick="calc.display.value='-'"> </td> <td><input id="btn" type="button" value="%" OnClick="calc.display.value+='%'"> </td> <td><input id="btn" type="button" value="cos" OnClick="calc.display.value='cos('"> </td> </tr> <tr> <td><input id="btn" type="button" value="7" OnClick="calc.display.value+='7'"> </td> <td><input id="btn" type="button" value="8" OnClick="calc.display.value+='8'"> </td> <td><input id="btn" type="button" value="9" OnClick="calc.display.value+='9'"> </td> <td><input id="btn" type="button" value="*" OnClick="calc.display.value+='*'"> </td> <td><input id="btn" type="button" value="n." OnClick="calc.display.value+='.'"> </td> <td><input id="btn" type="button" value="sin" OnClick="calc.display.value='Math.sin('"> </td> </tr> <tr> <td><input id="btn" type="button" value="." OnClick="calc.display.value+='.'"> </td> <td><input id="btn" type="button" value="0" OnClick="calc,display.value+='0'"> </td> <td><input id="btn" type="button" value="." OnClick="calc,display.value+='.'"> </td> <td><input id="btn" type="button" value="+" OnClick="calc.display.value+='+'"> </td> <td><input id="btn" type="button" value="/" OnClick="calc.display.value+='/'"> </td> <td><input id="btn" type="button" value="tan" OnClick="calc.display.value='Math.tan('"> </td> </tr> <tr> <td><input id="btn" type="button" value="E" OnClick="calc.display.value+='Math.E'"> </td> <td><input id="btn" type="button" value="pi" OnClick="calc.display.value+='Math.PI'"> </td> <td><input id="btn" type="button" value="^" OnClick="calc.display.value+='Math.pow('"> </td> <td><input id="btn" type="button" value="(" OnClick="calc.display.value+='('"> </td> <td><input id="btn" type="button" value=")" OnClick="calc.display.value+=')'"> </td> <td><input id="btn" type="button" value="log" OnClick="calc.display.value='Math.log('"> </td> </tr> <tr> <td><input id="btn" type="button" value="sqrt" OnClick="calc.display.value+='Math.sqrt('"> </td> <td><input id="btn" type="button" value="ln2" OnClick="calc.display.value+='Math.LN2'"> </td> <td><input id="btn" type="button" value="ln10" OnClick="calc.display.value+='Math.Log10'"> </td> <td><input id="btn" type="button" value="l2e" OnClick="calc.display.value+='Math.LOG2E'"> </td> <td><input id="btn" type="button" value="l10e" OnClick="calc.display.value+='Math.log10'"> </td> <td><input id="btn" type="button" value="exp" OnClick="calc.display.value='Math.exp('"> </td> </tr> </table> </form>