JavaScript truthy values referring to numbers

Question

JavaScript truthy values referring to numbers

According to the rules outlined below:

Falsy:

false
0 (zero)
'' or "" (empty string)
null
undefinded
NaN (e.g. the result of 1/0)

Truthy: Anything else

I'm puzzled as to why, in the tests that follow, only the number 1 is considered "true"

0 == true ("false")
1 == true ("true")
2 == true ("false")
othernumber == true ("false")

javascript equality

Answer 1

Answer №1

When it comes to the "truthy" and "falsy" rules, they are only applicable when the value itself is used as a test, as shown in this example:

var str = "";
if (str) {
    // It's considered truthy
} else {
    // It's considered falsy
}

The == operator operates under its own unique set of criteria for establishing the loose equality between its operands. These rules are extensively explained in the specifications's Abstract Equality Comparison algorithm:

If Type(x) matches Type(y), then

Return the result of performing Strict Equality Comparison x === y.

If x is null and y is undefined, return true.

If x is undefined and y is null, return true.

If Type(x) is Number and Type(y) is String, return the comparison result of x == ToNumber(y).

If Type(x) is String and Type(y) is Number, return the comparison result of ToNumber(x) == y.

If Type(x) is Boolean, return the comparison result of ToNumber(x) == y.

If Type(y) is Boolean, return the comparison result of x == ToNumber(y).

If Type(x) is either String, Number, or Symbol and Type(y) is Object, return the comparison result of x == ToPrimitive(y).

If Type(x) is Object and Type(y) is either String, Number, or Symbol, return the comparison result of ToPrimitive(x) == y.

Return false.

Refer to the specifications for a comprehensive understanding of the different abstract operations listed there. Although the names mostly indicate their functionality, it's worth noting that certain specifications like ! prior to ToNumber should not be confused with the logical NOT operator; rather, it is related to "abrupt completions." (Learn more here)

For instance, let's dissect the 2 == true scenario using these guidelines:

Since the types don't match, move on to the next step
x isn't null, proceed further
x isn't undefined, keep moving forward
Although Type(x) is Number, Type(y) is not a String, thus continue to the next step
Type(x) isn't String, proceed ahead
Type(x) isn't Boolean, keep going
As Type(y) is Boolean, we return the result of x == ToNumber(y)
- ToNumber(true) equals 1, so since 2 != 1, the outcome would be false

Now, observe how step 7 differs when dealing with the 1 == true situation:

Since Type(y) is Boolean, we now get the result of x == ToNumber(y)
- After evaluating ToNumber(true) as 1, it turns out that 1 == 1 is true, hence leading to a true result

Answer 2

When it comes to the "truthy" and "falsy" rules, they are only applicable when the value itself is used as a test, as shown in this example:

var str = "";
if (str) {
    // It's considered truthy
} else {
    // It's considered falsy
}

The == operator operates under its own unique set of criteria for establishing the loose equality between its operands. These rules are extensively explained in the specifications's Abstract Equality Comparison algorithm:

If Type(x) matches Type(y), then

Return the result of performing Strict Equality Comparison x === y.

If x is null and y is undefined, return true.

If x is undefined and y is null, return true.

If Type(x) is Number and Type(y) is String, return the comparison result of x == ToNumber(y).

If Type(x) is String and Type(y) is Number, return the comparison result of ToNumber(x) == y.

If Type(x) is Boolean, return the comparison result of ToNumber(x) == y.

If Type(y) is Boolean, return the comparison result of x == ToNumber(y).

If Type(x) is either String, Number, or Symbol and Type(y) is Object, return the comparison result of x == ToPrimitive(y).

If Type(x) is Object and Type(y) is either String, Number, or Symbol, return the comparison result of ToPrimitive(x) == y.

Return false.

Refer to the specifications for a comprehensive understanding of the different abstract operations listed there. Although the names mostly indicate their functionality, it's worth noting that certain specifications like ! prior to ToNumber should not be confused with the logical NOT operator; rather, it is related to "abrupt completions." (Learn more here)

For instance, let's dissect the 2 == true scenario using these guidelines:

Since the types don't match, move on to the next step
x isn't null, proceed further
x isn't undefined, keep moving forward
Although Type(x) is Number, Type(y) is not a String, thus continue to the next step
Type(x) isn't String, proceed ahead
Type(x) isn't Boolean, keep going
As Type(y) is Boolean, we return the result of x == ToNumber(y)
- ToNumber(true) equals 1, so since 2 != 1, the outcome would be false

Now, observe how step 7 differs when dealing with the 1 == true situation:

Since Type(y) is Boolean, we now get the result of x == ToNumber(y)
- After evaluating ToNumber(true) as 1, it turns out that 1 == 1 is true, hence leading to a true result

Answer 3

Answer №2

According to the information provided in this source, when comparing values to a boolean, such as in the syntax x == y, there is an interesting pattern that follows:

If Type(x) is Boolean, the comparison result will be of ToNumber(x) == y.

If Type(y) is Boolean, the comparison result will be x == ToNumber(y).

For instance, when evaluating 1 == true, it essentially translates to 1 == ToNumber(true), which then simplifies to 1 == 1. On the other hand, 2 == true gets converted to 2 == 1, resulting in false.

The book advises against comparing values directly to boolean types for various reasons presented within its content.

When making comparisons involving booleans, it's important to note that even if the value appears truthy or falsy, it undergoes coercion into a type compatible with the boolean counterpart to enable the use of the == operator.

I trust this explanation meets your expectations.

Answer 4

According to the information provided in this source, when comparing values to a boolean, such as in the syntax x == y, there is an interesting pattern that follows:

If Type(x) is Boolean, the comparison result will be of ToNumber(x) == y.

If Type(y) is Boolean, the comparison result will be x == ToNumber(y).

For instance, when evaluating 1 == true, it essentially translates to 1 == ToNumber(true), which then simplifies to 1 == 1. On the other hand, 2 == true gets converted to 2 == 1, resulting in false.

The book advises against comparing values directly to boolean types for various reasons presented within its content.

When making comparisons involving booleans, it's important to note that even if the value appears truthy or falsy, it undergoes coercion into a type compatible with the boolean counterpart to enable the use of the == operator.

I trust this explanation meets your expectations.

Answer 5

Answer №3

Using == is not the same as using if(something). To see the difference in action, try running this test:

function trueFalseTest()
{
    if(0) 
    {
       console.log("true");
    }
    else
    {
        console.log("false");
    }

    if(1) 
    {
       console.log("true");
    }
    else
    {
        console.log("false");
    }

    if(2) 
    {
       console.log("true");
    }
    else
    {
        console.log("false");
    }

    if(2222) 
    {
       console.log("true");
    }
    else
    {
        console.log("false");
    }
}

trueFalseTest();

Answer 6

Using == is not the same as using if(something). To see the difference in action, try running this test:

function trueFalseTest()
{
    if(0) 
    {
       console.log("true");
    }
    else
    {
        console.log("false");
    }

    if(1) 
    {
       console.log("true");
    }
    else
    {
        console.log("false");
    }

    if(2) 
    {
       console.log("true");
    }
    else
    {
        console.log("false");
    }

    if(2222) 
    {
       console.log("true");
    }
    else
    {
        console.log("false");
    }
}

trueFalseTest();

Answer 7

Answer №4

When it comes to equality in JavaScript, the (==) operator is used for checking equality with type conversion, while the (===) operator is more strict and does not perform type conversion.

For instance, you can pass a number where a boolean is expected when using (==), even though they are different data types.

However, if you opt for the strict (===) operator, you will find that '1 === true' results in false because it does not allow type conversion.

Answer 8

When it comes to equality in JavaScript, the (==) operator is used for checking equality with type conversion, while the (===) operator is more strict and does not perform type conversion.

For instance, you can pass a number where a boolean is expected when using (==), even though they are different data types.

However, if you opt for the strict (===) operator, you will find that '1 === true' results in false because it does not allow type conversion.

Answer 9

Answer №5

It's important to remember that just because 0 is false, it doesn't mean other numbers will be true. For example, using === in a condition will result in false for all numbers.

(0 == true) // false
(1 == true) // true

Surprisingly, even without the not operator (!), the results can still be unexpected. If the condition is true, it should print true, otherwise false. Yet, you may still end up with the opposite outcome.

if(0){console.log("true")}else{console.log("false")} // false
if(1){console.log("true")}else{console.log("false")} // true
if(15){console.log("true")}else{console.log("false")} // true

However, converting numbers to Boolean will yield the expected results that align with your initial thoughts.

Boolean(0) == true // false
Boolean(1) == true // true
Boolean(2) == true // true
Boolean(othernumber) == true // true

Thank you

Answer 10

It's important to remember that just because 0 is false, it doesn't mean other numbers will be true. For example, using === in a condition will result in false for all numbers.

(0 == true) // false
(1 == true) // true

Surprisingly, even without the not operator (!), the results can still be unexpected. If the condition is true, it should print true, otherwise false. Yet, you may still end up with the opposite outcome.

if(0){console.log("true")}else{console.log("false")} // false
if(1){console.log("true")}else{console.log("false")} // true
if(15){console.log("true")}else{console.log("false")} // true

However, converting numbers to Boolean will yield the expected results that align with your initial thoughts.

Boolean(0) == true // false
Boolean(1) == true // true
Boolean(2) == true // true
Boolean(othernumber) == true // true

Thank you

Answer 11

Answer №6

Following these guidelines: The current issue is that the == operator does not follow these guidelines. The concept of truthiness and how it behaves in equality tests are distinct from each other. For clarity, a more accurate truthiness test would be:

if (value) 
    return true;
else
    return false;

Alternatively, a concise conversion like Boolean(value) or the implicit conversion !!value can also be used.

However, during an equality comparison, both operands of == will be coerced to the same base type before the actual comparison takes place. Referencing MDN's rules for conversion, particularly in cases like 1 == true where one operand is a number and the other is a boolean, both will be converted to the base type of number before comparison using ToNumber(booleanValue).

var convertedBooleanOperand = Number(true);

console.log("convertedBooleanOperand", convertedBooleanOperand);

In essence, 2 == true gets converted to 2 == 1 which results in false.

Answer 12

Following these guidelines: The current issue is that the == operator does not follow these guidelines. The concept of truthiness and how it behaves in equality tests are distinct from each other. For clarity, a more accurate truthiness test would be:

if (value) 
    return true;
else
    return false;

Alternatively, a concise conversion like Boolean(value) or the implicit conversion !!value can also be used.

However, during an equality comparison, both operands of == will be coerced to the same base type before the actual comparison takes place. Referencing MDN's rules for conversion, particularly in cases like 1 == true where one operand is a number and the other is a boolean, both will be converted to the base type of number before comparison using ToNumber(booleanValue).

var convertedBooleanOperand = Number(true);

console.log("convertedBooleanOperand", convertedBooleanOperand);

In essence, 2 == true gets converted to 2 == 1 which results in false.

JavaScript truthy values referring to numbers

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

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