IE11 的 Math.pow 替代“**”ES7 polyfill

Question

I'm trying to evaluate an expression which contains power, in string as ** . ie eval("(22**3)/12*6+3/2") .The problem is Internet Explorer 11 does not recognizes this and throws syntax error. Which poly-fill I should use to overcome this? Right now I'm using Modernizr 2.6.2 .

example equation would be,

((1*2)*((3*(4*5)*(1+3)**(4*5))/((1+3)**(4*5)-1)-1)/6)/7
((1*2)*((3*(4*5)*(1+3)**(4*5))/((1+3)**(4*5)-1)-1)/6)/7*58+2*5
(4*5+4-5.5*5.21+14*36**2+69/0.258+2)/(12+65)

If it is not possible to do this, what are the possible alternatives?

Answer 1

You cannot polyfill operators - only library members (prototypes, constructors, properties).

As your operation is confined to an eval call, you could attempt to write your own expression parser, but that would be a lot of work.

(As an aside, you shouldn't be using eval anyway, for very good reasons that I won't get into in this posting).

Another (hack-ish) option is to use a regular expression to identify trivial cases of x**y and convert them to Math.pow :

function detectAndFixTrivialPow( expressionString ) {

    var pattern = /(\w+)\*\*(\w+)/i;

    var fixed = expressionString.replace( pattern, 'Math.pow($1,$2)' );
    return fixed;
}

eval( detectAndFixTrivialPow( "foo**bar" ) );

Answer 2

You can use a regular expression to replace the occurrences of ** with Math.pow() invocations:

 let expression = "(22**3)/12*6+3/2" let processed = expression.replace(/(\w+)\*\*(\w+)/g, 'Math.pow($1,$2)'); console.log(processed); console.log(eval(processed));

Things might get complicated if you start using nested or chained power expressions though.

Answer 3

I think you need to do some preprocessing of the input. Here is how i would approach this:

1. Find "**" in string.
2. Check what is on the left and right.
3. Extract "full expressions" from left and right - if there is just a number - take it as is, and if there is a bracket - find the matching one and take whatever is inside as an expression.
4. Replace the 2 expressions with Math.pow(left, right)

Answer 4

您可以在线使用 Babel为 IE 11 转换 javascript。