如何在javascript中优化此if-else语句

Question

I have a piece of javascript code like this

        if(prog > 100)
          prog = 100;
        else if(prog <0)
          prog = 0;
        else if(typeof prog != 'number')
          prog = 0;

It looks bad and ugly. Is there some cooler way to write this in javascript?

Answer 1

prog = Math.max(0, Math.min(100, typeof prog == 'number' ? prog : 0));

Answer 2

How about this:

 foo = typeof foo == "number" ? foo : 0;
 foo.constrain(0, 100);

Which would simply require this to be defined:

Number.prototype.constrain = function(min, max) {
  return Math.min(max, Math.max(min, this.valueOf())); 
}

Answer 3

prog = (prog > 100 ? 100 : (prog<0 || (typeof prog != 'number') ? 0 : prog));

jsfiddle

Answer 4

if(typeof prog != 'number' || prog < 0){
    prog = 0;
} else if (prog > 100) {
    prog = 100;
}

• if prog is not a number, or less than 0, set to zero right off the bat
• else if prog is greater than 100, set 100
• anything else, it leaves it alone

the issue was you were evaluating a variable as a number without knowing that it's a number (since you placed the typeof check last). if i were to pass foo to prog , you'd be evaluating 2 times before checking the type. also, you were evaluating two conditions for the same output of 0 , better merge them.

JS does not evaluate the OR further when it sees a TRUE in the condition. likewise can be said for the AND when it sees a FALSE .

Answer 5

Really you should test the type first:

if ( typeof prog != 'number' || prog < 0 )
   prog = 0;
else if( prog > 100 )
   prog = 100;

Double ternary:

prog = typeof prog != 'number'?0:prog;
prog = (prog>100)?100:((prog<0)?0:prog);

Answer 6

Here is my take. It is functionally equivalent, and concise, but not the legible when you come back to the code 12 months from now.

prog = (typeof prog != 'number' || prog < 0 ? 0 : (prog > 100 ? 100 : prog));

UPDATE

Here are a couple other ways to do this.

prog = (typeof prog != 'number' ? 0 : Math.max(0,Math.min(prog, 100)));
prog = (typeof prog != 'number' || prog < 0 ? 0 : Math.min(prog, 100));

I think the first of these two is probably the easiest to understand. Basically, if it isn't a number it sets it to 0 , else it makes sure it is between 0 and 100 which seems to be the logic you are really going after.