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##Some points

• Put magic numbers in constants to give them meaning.
• Variables that do not change should be defined as constants
• Use appropriate Array functions rather than iterating over the array.
• Math.round only takes one argument. I do not know why you pass 2 as a second argument. If I guess you want to round to 2 decimal places. To do that you can use Number.toFixed() however that returns the number as a String so to be safe and return the same type you would use Number(BMI.toFixed(2)) or you can use Math.round(BMI * 100) / 100
• You can use the ** operator to raise a value to a power.

##Examples

const computeBMI = (weight, height, country) => {
 const FEET_2_METERS = 0.3048;
 const BMI_SCALE = 0.82;
 const COUNTRIES = ["Chad", "Sierra Leone", "Mali", "Gambia", "Uganda", "Ghana", "Senegal", "Somalia", "Ivory Coast", "Isreal"];
 return Math.round(weight / (height * FEET_2_METERS) ** 2 *
 (COUNTRIES.includes(country) ? BMI_SCALE : 1));
 
};

Though it would be better to have the constants held in closure if you are to use them in other functions.

const compute = (()=> {
 const FEET_2_METERS = 0.3048;
 const BMI_SCALE = 0.82;
 const COUNTRIES = ["Chad", "Sierra Leone", "Mali", "Gambia", "Uganda", "Ghana", "Senegal", "Somalia", "Ivory Coast", "Isreal"]; 
 return {
 BMI(weight, height, country) {
 return Math.round(weight / (height * FEET_2_METERS) ** 2 * (COUNTRIES.includes(country) ? BMI_SCALE : 1));
 }
 };
})();
compute.BMI(90, 6.2, "Somewhere");

Some points

• Put magic numbers in constants to give them meaning.
• Variables that do not change should be defined as constants
• Use appropriate Array functions rather than iterating over the array.
• Math.round only takes one argument. I do not know why you pass 2 as a second argument. If I guess you want to round to 2 decimal places. To do that you can use Number.toFixed() however that returns the number as a String so to be safe and return the same type you would use Number(BMI.toFixed(2)) or you can use Math.round(BMI * 100) / 100
• You can use the ** operator to raise a value to a power.

Examples

const computeBMI = (weight, height, country) => {
 const FEET_2_METERS = 0.3048;
 const BMI_SCALE = 0.82;
 const COUNTRIES = ["Chad", "Sierra Leone", "Mali", "Gambia", "Uganda", "Ghana", "Senegal", "Somalia", "Ivory Coast", "Isreal"];
 return Math.round(weight / (height * FEET_2_METERS) ** 2 *
 (COUNTRIES.includes(country) ? BMI_SCALE : 1));
 
};

Though it would be better to have the constants held in closure if you are to use them in other functions.

const compute = (()=> {
 const FEET_2_METERS = 0.3048;
 const BMI_SCALE = 0.82;
 const COUNTRIES = ["Chad", "Sierra Leone", "Mali", "Gambia", "Uganda", "Ghana", "Senegal", "Somalia", "Ivory Coast", "Isreal"]; 
 return {
 BMI(weight, height, country) {
 return Math.round(weight / (height * FEET_2_METERS) ** 2 * (COUNTRIES.includes(country) ? BMI_SCALE : 1));
 }
 };
})();
compute.BMI(90, 6.2, "Somewhere");