Why doesn't my equality comparison using = (a single equals) work correctly? [duplicate]
This question already has an answer here:
Why doesn't my simple if-statement render false in javascript?
2 answers
I'm trying to check if a string is blank, less than or equal to 9 digits, or up to 10 digits. But it always follows the else if (str.length <= 9).
if (str = ''){
console.log("The string cannot be blank");
} else if (str.length <= 9) {
console.log("The string must be at least 9 characters long");
} else if (str.length <= 10) {
console.log("The string is long enough.");
}
No matter what I put in, I always get The string must be at least 9 characters long. Why?
javascript equality
edited Jul 8 '16 at 13:57
T.J. Crowder
681k12112061302
asked Jul 8 '16 at 13:48
SamSam
195
marked as duplicate by Oriol javascript
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Dec 15 '16 at 18:30
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
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This question already has an answer here:
Why doesn't my simple if-statement render false in javascript?
2 answers
I'm trying to check if a string is blank, less than or equal to 9 digits, or up to 10 digits. But it always follows the else if (str.length <= 9).
if (str = ''){
console.log("The string cannot be blank");
} else if (str.length <= 9) {
console.log("The string must be at least 9 characters long");
} else if (str.length <= 10) {
console.log("The string is long enough.");
}
No matter what I put in, I always get The string must be at least 9 characters long. Why?
javascript equality
edited Jul 8 '16 at 13:57
T.J. Crowder
681k12112061302
asked Jul 8 '16 at 13:48
SamSam
195
marked as duplicate by Oriol javascript
Users with the javascript badge can single-handedly close javascript questions as duplicates and reopen them as needed.
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Dec 15 '16 at 18:30
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
2
I'm sure there must be a canonical question for this...
– T.J. Crowder
Jul 8 '16 at 13:50
1
@T.J.Crowder — Possibly, but I'd be surprised if any of them had a title as clear as this one. Mostly they come to do "My code doesn't work and I don't know why"
– Quentin
Jul 8 '16 at 13:54
@Quentin: Yeah. I'm editing this into one. :-)
– T.J. Crowder
Jul 8 '16 at 13:54
@T.J.Crowder — Ooops, didn't notice that was your edit :)
– Quentin
Jul 8 '16 at 13:55
@Quentin: No worries, that's a better title
– T.J. Crowder
Jul 8 '16 at 13:57
|
show 2 more comments
This question already has an answer here:
Why doesn't my simple if-statement render false in javascript?
2 answers
I'm trying to check if a string is blank, less than or equal to 9 digits, or up to 10 digits. But it always follows the else if (str.length <= 9).
if (str = ''){
console.log("The string cannot be blank");
} else if (str.length <= 9) {
console.log("The string must be at least 9 characters long");
} else if (str.length <= 10) {
console.log("The string is long enough.");
}
No matter what I put in, I always get The string must be at least 9 characters long. Why?
javascript equality
edited Jul 8 '16 at 13:57
T.J. Crowder
681k12112061302
asked Jul 8 '16 at 13:48
SamSam
195
This question already has an answer here:
Why doesn't my simple if-statement render false in javascript?
2 answers
I'm trying to check if a string is blank, less than or equal to 9 digits, or up to 10 digits. But it always follows the else if (str.length <= 9).
if (str = ''){
console.log("The string cannot be blank");
} else if (str.length <= 9) {
console.log("The string must be at least 9 characters long");
} else if (str.length <= 10) {
console.log("The string is long enough.");
}
No matter what I put in, I always get The string must be at least 9 characters long. Why?
This question already has an answer here:
Why doesn't my simple if-statement render false in javascript?
2 answers
javascript equality
javascript equality
edited Jul 8 '16 at 13:57
T.J. Crowder
681k12112061302
asked Jul 8 '16 at 13:48
SamSam
195
edited Jul 8 '16 at 13:57
T.J. Crowder
681k12112061302
asked Jul 8 '16 at 13:48
SamSam
195
edited Jul 8 '16 at 13:57
T.J. Crowder
681k12112061302
edited Jul 8 '16 at 13:57
T.J. Crowder
681k12112061302
edited Jul 8 '16 at 13:57
T.J. Crowder
681k12112061302
681k12112061302
asked Jul 8 '16 at 13:48
SamSam
195
asked Jul 8 '16 at 13:48
SamSam
195
asked Jul 8 '16 at 13:48
SamSam
195
195
marked as duplicate by Oriol javascript
Users with the javascript badge can single-handedly close javascript questions as duplicates and reopen them as needed.
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Dec 15 '16 at 18:30
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
marked as duplicate by Oriol javascript
Users with the javascript badge can single-handedly close javascript questions as duplicates and reopen them as needed.
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Dec 15 '16 at 18:30
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
2
I'm sure there must be a canonical question for this...
– T.J. Crowder
Jul 8 '16 at 13:50
1
@T.J.Crowder — Possibly, but I'd be surprised if any of them had a title as clear as this one. Mostly they come to do "My code doesn't work and I don't know why"
– Quentin
Jul 8 '16 at 13:54
@Quentin: Yeah. I'm editing this into one. :-)
– T.J. Crowder
Jul 8 '16 at 13:54
@T.J.Crowder — Ooops, didn't notice that was your edit :)
– Quentin
Jul 8 '16 at 13:55
@Quentin: No worries, that's a better title
– T.J. Crowder
Jul 8 '16 at 13:57
|
show 2 more comments
2
I'm sure there must be a canonical question for this...
– T.J. Crowder
Jul 8 '16 at 13:50
1
@T.J.Crowder — Possibly, but I'd be surprised if any of them had a title as clear as this one. Mostly they come to do "My code doesn't work and I don't know why"
– Quentin
Jul 8 '16 at 13:54
@Quentin: Yeah. I'm editing this into one. :-)
– T.J. Crowder
Jul 8 '16 at 13:54
@T.J.Crowder — Ooops, didn't notice that was your edit :)
– Quentin
Jul 8 '16 at 13:55
@Quentin: No worries, that's a better title
– T.J. Crowder
Jul 8 '16 at 13:57
2
2
I'm sure there must be a canonical question for this...
– T.J. Crowder
Jul 8 '16 at 13:50
I'm sure there must be a canonical question for this...
– T.J. Crowder
Jul 8 '16 at 13:50
1
1
@T.J.Crowder — Possibly, but I'd be surprised if any of them had a title as clear as this one. Mostly they come to do "My code doesn't work and I don't know why"
– Quentin
Jul 8 '16 at 13:54
@T.J.Crowder — Possibly, but I'd be surprised if any of them had a title as clear as this one. Mostly they come to do "My code doesn't work and I don't know why"
– Quentin
Jul 8 '16 at 13:54
@Quentin: Yeah. I'm editing this into one. :-)
– T.J. Crowder
Jul 8 '16 at 13:54
@Quentin: Yeah. I'm editing this into one. :-)
– T.J. Crowder
Jul 8 '16 at 13:54
@T.J.Crowder — Ooops, didn't notice that was your edit :)
– Quentin
Jul 8 '16 at 13:55
@T.J.Crowder — Ooops, didn't notice that was your edit :)
– Quentin
Jul 8 '16 at 13:55
@Quentin: No worries, that's a better title
– T.J. Crowder
Jul 8 '16 at 13:57
@Quentin: No worries, that's a better title
– T.J. Crowder
Jul 8 '16 at 13:57
|
show 2 more comments
1 Answer
1
active
oldest
votes
= is always assignment. Equality comparison is == (loose, coerces types to try to make a match) or === (no type coercion).
So you want
if (str === ''){
// -----^^^
not
// NOT THIS
if (str = ''){
// -----^
What happens when you do if (str = '') is that the assignment str = '' is done, and then the resulting value ('') is tested, effectively like this (if we ignore a couple of details):
str = '';
if (str) {
Since '' is a falsy value in JavaScript, that check will be false and it goes to the else if (str.length <= 9) step. Since at that point, str.length is 0, that's the path the code takes.
add a comment |
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
= is always assignment. Equality comparison is == (loose, coerces types to try to make a match) or === (no type coercion).
So you want
if (str === ''){
// -----^^^
not
// NOT THIS
if (str = ''){
// -----^
What happens when you do if (str = '') is that the assignment str = '' is done, and then the resulting value ('') is tested, effectively like this (if we ignore a couple of details):
str = '';
if (str) {
Since '' is a falsy value in JavaScript, that check will be false and it goes to the else if (str.length <= 9) step. Since at that point, str.length is 0, that's the path the code takes.
add a comment |
= is always assignment. Equality comparison is == (loose, coerces types to try to make a match) or === (no type coercion).
So you want
if (str === ''){
// -----^^^
not
// NOT THIS
if (str = ''){
// -----^
What happens when you do if (str = '') is that the assignment str = '' is done, and then the resulting value ('') is tested, effectively like this (if we ignore a couple of details):
str = '';
if (str) {
Since '' is a falsy value in JavaScript, that check will be false and it goes to the else if (str.length <= 9) step. Since at that point, str.length is 0, that's the path the code takes.
add a comment |
= is always assignment. Equality comparison is == (loose, coerces types to try to make a match) or === (no type coercion).
So you want
if (str === ''){
// -----^^^
not
// NOT THIS
if (str = ''){
// -----^
What happens when you do if (str = '') is that the assignment str = '' is done, and then the resulting value ('') is tested, effectively like this (if we ignore a couple of details):
str = '';
if (str) {
Since '' is a falsy value in JavaScript, that check will be false and it goes to the else if (str.length <= 9) step. Since at that point, str.length is 0, that's the path the code takes.
= is always assignment. Equality comparison is == (loose, coerces types to try to make a match) or === (no type coercion).
So you want
if (str === ''){
// -----^^^
not
// NOT THIS
if (str = ''){
// -----^
What happens when you do if (str = '') is that the assignment str = '' is done, and then the resulting value ('') is tested, effectively like this (if we ignore a couple of details):
str = '';
if (str) {
Since '' is a falsy value in JavaScript, that check will be false and it goes to the else if (str.length <= 9) step. Since at that point, str.length is 0, that's the path the code takes.
edited Jul 8 '16 at 14:00
community wiki
3 revs
T.J. Crowder
add a comment |
add a comment |
2
I'm sure there must be a canonical question for this...
– T.J. Crowder
Jul 8 '16 at 13:50
1
@T.J.Crowder — Possibly, but I'd be surprised if any of them had a title as clear as this one. Mostly they come to do "My code doesn't work and I don't know why"
– Quentin
Jul 8 '16 at 13:54
@Quentin: Yeah. I'm editing this into one. :-)
– T.J. Crowder
Jul 8 '16 at 13:54
@T.J.Crowder — Ooops, didn't notice that was your edit :)
– Quentin
Jul 8 '16 at 13:55
@Quentin: No worries, that's a better title
– T.J. Crowder
Jul 8 '16 at 13:57