[Learning]#15 JS: if else statement

To make the operators meaningful for users, let’s explain by examples

if statement

If the statement is true, the code inside of {} would be executed.
On the contrary, it would be ignored when it’s false.

var money=prompt("How much money would you like to withdraw?");
if(money>30000) {
    alert("You've reached the withdraw money limit within a day.");
}

if else statement

Following the statement above, if the first statement is false, else {} would be executed.

var money=prompt("How much money would you like to withdraw?", "");
if(money>30000) {
    alert("You've reached the withdraw money limit within a day.");
}else{
    alert("Your money is preparing. Don't forget your ATM card.");
}

if else statement (multiple filters)

Following the 2nd statement, when we need more filters to execute the statements, that is, if both of the first statement and the former else if {} are false, the latter else if {} would be executed until the value complies with the string.

var n=prompt("How much money would you like to withdraw?", "");
if(n>500) {
    alert(n+">500");
}else if (n>300){
    alert(n+">300");
}else if (n>150){
    alert(n+">150");
}else {
    alert(n+"<=150");
}

Example

var n1=prompt("Please key in a random number.","");
var n2=prompt("Please key in a random number.","");
var op=prompt("Please key in a math symbol: +, -, *, /",""); //op = operator
var result;
if(op=="+") {
    result=n1+n2;
}else if (op=="-"){
    result=n1-n2;
}else if (op=="*"){
    result=n1*n2;
}else if (op=="/"){
    result=n1/n2;
}else {
    result="This operator does not comply with the rule.";
}
alert(result);

However, the number user keys in would be considered as a string, like “7” instead of purely 7, so if n1 is “7”, n2 is “7”, and the symbol is +, the result would be 77 instead of 14.

To change the data type, we have to transfer it from string to number by storing a function — Number — into the variable. (Not sure if it’s called function here? Please correct me if I’m wrong. Thank you.)

var n1=prompt("Please key in a random number.","");
var n2=prompt("Please key in a random number.","");

n1=Number(n1);
n2=Number(n2);

var op=prompt("Please key in a math symbol: +, -, *, /",""); //op = operator
var result;
if(op=="+") {
    result=n1+n2;
}else if (op=="-"){
    result=n1-n2;
}else if (op=="*"){
    result=n1*n2;
}else if (op=="/"){
    result=n1/n2;
}else {
    result="This operator does not comply with the rule.";
}
alert(result);

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