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The Details Part 3 We will now break apart the code that will replace work magic forward! from the previous page. Let's first assume that the function is called using the following: string_out = searchandreplace("The dog is chasing the mouse. The dog loves to eat mice.", "dog", "cat");
For the line-by-line breakdown I will be giving the code, then a short description of what is happening. var pos = the_string.indexOf(search_string); Set the variable pos to the beginning index of where the first "dog" is located in the string. Since the first character "T" has an index of 0, pos is now set to 4. This corresponds to the location of the first character in the search string. If the search string cannot be found in the string, pos is set to -1 and the following loop is never executed. while (pos>= 0) {
Start a loop that will stop when the variable pos is less than 0. found++; Increment the variable found. This is the same as found = found + 1. var start_string = the_string.substr(0, pos); Start breaking up the string by first finding the beginning section of the string. The variable start_string is set to "The ". var end_string = the_string.substr(pos + search_string.length); Find the ending section of the string. The variable end_string is set to " is chasing the mouse. The dog loves to eat mice.". the_string = start_string + replace_string + end_string; Put the string back together, adding in the replace string between the start string and end string. You've just replaced the first occurrence of "dog" with "cat"! The string is now "The cat is chasing the mouse. The dog loves to eat mice." Notice that the second occurrence of "dog" has not yet been replaced. pos = the_string.indexOf(search_string, pos + replace_string.length); Set the variable pos to the beginning index of the next "dog", but begin after the replacement string (just in case the replacement string includes the word "dog" and we end up in an endless loop). Since there is one more occurrence of the word "dog", we will start back at the while loop and go through one more time. Once "dog" cannot be found, pos is set to -1 and the looping stops. if (found == occurrences) {
pos = -1;
}
Check to see if we need to stop looking for occurrences. Once we have found all of the occurrences specified by the argument occurrences, we can set pos to -1 and stop the looping. If the argument occurrences is not given, all occurrences are replaced. This is because occurrences now equals null and found == occurrences will never be true. } Just add that last curly bracket to close up the loop.
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Search and Replace String 1.0
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